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Hibrarp 


A 

TEXT-BOOK  OF 
HISTOLOGY 


BY 

FREDERICK  R.  BAILEY.  A.  M.,  M.  D. 


THIRD  REVISED  EDITION 

PROFUSELY  ILLUSTRATED 


NEW   YORK 
WILLIAM   WOOD  AND   COMPANY 

M  D  C  C  C  C  X 


Copyright,   1910 
By  WILLIAM  WOOD  AND  COMPANY 


/'rill ted   by 

The  Maple  Press 

y„rk.  Pa. 


PREFACE   TO   THE   THIRD    EDITION. 


The  very  gratifying  approval  which  the  first  and  second  editions 
of  the  Text-book  received  has  made  it  seem  unwise  to  attempt  any 
change  in  the  general  plan  and  scope  of  the  work  as  outlined  in  the 
preface  to  the  first  edition.  The  text  has  been  thoroughly  revised, 
some  parts  of  it  practically  rewritten.  Some  figures  have  been 
replaced  by  new  ones  and  a  considerable  number  of  new  figures,  some 
original,  others  borrowed,  have  been  added.  For  the  latter  the  writer 
wishes  to  acknowledge  his  obligations.  To  Mr.  A.  M.  Miller  the 
writer  is  indebted  for  many  valuable  criticisms  and  suggestions.  The 
chapter  on  the  nervous  system  has  been  rewritten  by  Dr.  Oliver  S. 
Strong.  For  Dr.  Strong's  careful  and  painstaking  work  on  this  chapter, 
for  his  thoroughly  original  treatment  of  his  subject,  and  for  the  original 
drawings  and  photographs  in  this  chapter,  the  author  wishes  to  express 
his  most  grateful  appreciation.  Dr.  Strong  wishes  to  renew  the 
acknowledgment,  made  in  the  preface  to  Bailey  and  Miller's  Embryol- 
ogy, of  indebtedness  to  Dr.  Adolf  Meyer  for  many  ideas  and  terms 
found  valuable  in  the  preparation  of  the  chapter  on  the  nervous  system. 
There  may  be  mentioned  here  the  terms  segmental  and  supraseg- 
mental  to  denote  an  imjjortant  distinction  between  certain  }:)arts  of 
the  nervous  system. 


in 


Digitized  by  tine  Internet  Archive 

in  2010  with  funding  from 
Columbia  University  Libraries 


http://www.archive.org/details/textbookofhistol1910bail 


PREFACE    TO    THE    FIRST    EDITION. 


The  primary  aim  of  the  writer  in  the  preparation  of  these  pages 
has  been  to  give  to  the  student  of  medicine  a  text-book  of  histology 
for  use  in  connection  with  practical  laboratory  instruction,  and  espe- 
cially to  furnish  to  the  instructor  of  histology  a  satisfactory  manual 
for  classroom  teaching.  With  these  objects  in  view,  the  text  has 
been  made  as  concise  as  possible  consistent  with  clearness,  and  the 
writer  has  attempted  to  make  the  more  essential  elements  stand  out 
somewhat  from  the  necessarily  accompanying  details. 

It  has  been  impossible  to  accomplish  this  without  some  sacrifice 
of  uniformity  of  treatment  and  of  logical  sequence.  This  is  espe- 
cially noticeable  in  the  chapter  on  the  nervous  system,  which  has  been 
made  much  fuller  and  more  "practical"  than  is  usual.  The  author's 
reason  for  the  method  of  treatment  there  adopted  and  for  the  consider- 
able amount  of  anatomy  which  this  chapter  contains  being  the  apparent 
success  the  method  has  met  with  in  the  teaching  of  this  always  ditiicult 
subject  to  students. 

The  chapter  on  general  technic  is  intended  to  furnish  the  student 
with  only  the  more  essential  laboratory  methods.  For  special  and 
more  elaborate  methods  the  student  is  referred  to  the  special  works 
on  technic  mentioned  at  the  close  of  the  chapter.  The  special  technic 
given  in  connection  with  the  different  tissues  and  organs  is  in  most 
cases  such  as  can  be  conveniently  used  for  the  preparation  of  class 
sections. 

The  original  illustrations  are  from  drawings  by  Mr.  A.  M.  ^SLiller, 
to  whom  the  writer  is  greatly  indebted  for  his  careful  and  accurate 
work.  The  uselessness  of  redrawing  perfectly  satisfactory  illustra- 
tions has  led  the  writer  to  borrow  freely  from  various  sources,  each  cut 
being  duly  accredited  to  the  work  from  which  it  has  l^een  taken.     For 


vi  PREFACE. 

all  of  these  the  author  wishes  to  express  his  appreciation  and  obligation. 
He  is  also  deeply  indebted  to  Dr.  O.  S.  Strong  for  his  careful  review 
and  criticism  of  the  chapter  on  the  nervous  system  and  for  his  super- 
vision of  the  drawing  of  Figs.  263  and  264;  to  Dr.  G.  C.  Freeborn, 
his  predecessor  as  Instructor  of  Histology  at  the  College  of  Physicians 
and  Surgeons,  for  many  valuable  suggestions;  and  to  Dr.  T.  Mitchell 
Prudden  for  his  careful  and  critical  review  of  the  author's  copy. 


CONTENTS. 


PART  I.— HISTOLOGICAL  TECHNIC. 

CHAPTER    I. 


PAGE 


General  Technic. 

General  Considerations, 3 

Examination  of  Fresh  Tissues, 3 

Dissociation  of  Tissue  Elements, 4 

Teasing, 4 

Maceration 4 

Preparation  of  Sections, 5 

Fixation, 5 

Hardening, 8 

Preserving, 9 

Decalcifying, .  9 

Embedding, 10 

Celloidin  Embedding,       11 

Paraffin  Embedding, 12 

Section  Cutting,        13 

Celloidin  Sections, 14 

Paraffin  Sections, 14 

Staining, 15 

Nuclear  Dyes,       15 

Plasma  Dyes 17 

Staining  Sections, 18 

Staining  in  Bulk 19 

Mounting, 20 

Staining  and  Mounting  Paraffin  Sections, 21 

Injection, 22 

CHAPTER    II. 

Special  Staining  Methods. 

Silver  Nitrate  Method  of  Staining  the  Intercellular  Substance,       .    .  26 

Chlorid  of  Gold  for  Demonstrating  Connective-tissue  Cells,     ....  26 

Weigert's  Elastic  Tissue  Stain,       26 

Golgi's  Chrome-silver  for  Staining  Secretory  Tubules, 26 

Mallory's  Phosphomolybdic  Acid  Haematoxylin  Stain  for  Connective 

Tissue 27 

vii 


CONTENTS. 

PAGE 

Mallory's  Phosphotungstic  Acid  Hsematoxylin    Stain  for  Connective 

Tissue, 27 

Mallory's  Aniline  Blue  Stain  for  Connective  Tissue        28 

Osmic  Acid  Stain  for  Fat, 28 

Jenner's  Blood  Stain,       28 


CHAPTER    III. 

Special  Neurological  Staining  Methods. 

Weigert's  Method  of  Staining  Medullated  Nerve  Fibres, 29 

Weigert-Pal  Method,        30 

Marchi's  Method  for  Staining  Degenerating  Nerves, 31 

Golgi  Methods  of  Staining  Nerve  Tissue, 32 

Slow  Method, 32 

Rapid  Method, 32 

Mixed  Method 32 

Formalin  bichromate  Method, ^^ 

Bichloride  Method,      33 

Golgi-Cox  Method,       33 

Cajal's  Method 34 

Nissl's  Method, 35 

General  References  on  Technic, 35 


PART  II.— THE  CELL. 


CHAPTER    I. 

The  Cell, 39 

General  Structure, 39 

Structure  of  a  Typical  Cell, 39 

The  Cell  Body, 40 

The  Cell  Membrane, 42 

The  Nucleus, 42 

The  Centrosome,       44 

Vital  Properties  of  Cells, 45 

Metabolism, 45 

Function,       46 

Irritability, 46 

Motion 46 

Amoeboid, 46 

Protoplasmic, 47 

Ciliary,       47 

Reproduction 47 

Direct  Cell-division, 47 

Indirect  Cell-division, 48 

Fertilization  of  the  Ovum, 52 

Technic, 57 

References  for  further  study, 58 


CONTENTS- 


PART  III.— THE  TISSUES, 


CHAPTER    I. 

PAGE 

Histogenesis- — Classification 6i 

Tissues  Derived  from  Ectoderm,       .  • 6i 

Tissues  Derived  from  Entoderm, 6i 

Tissues  Derived  from  Mesoderm, 6i 


CHAPTER    IT 

Epithelium  (Including  Mesothelium  and  Endothelium), 63 

Histogenesis, 63 

General  Characteristics,       63 

Classification, 64 

Simple  Epithelium, 64 

Simple  Squamous, 64 

Simple  Columnar 65 

Pseudostratified, 65 

Stratified  Epithelium, 66 

Stratified  Squamous,        66 

Stratified  Columnar, 67 

Transitional, 67 

Modified  Forms  of  Epithelium, 68 

Ciliated  Epithelium, 68 

Pigmented  Epithelium,        69 

Glandular  Epithelium, 69 

Neuro-epithelium, 69 

Mesothelium  and  Endothelium, 70 

Technic, 71 


CHAPTER    III. 

The  Connective  Tissues, 73 

Histogenesis, 73 

General  Characteristics,       73 

Classification, 74 

Fibrillar  Connective  Tissue, 74 

Areolar  Connective  Tissue, 77 

Formed  Connective  Tissue 78 

Development,        78 

Elastic  Tissue 78 

Technic  for  Fibrillar  and  Elastic  Tissue, 80 

Embryonal  and  Mucous  Tissue, 81 

Technic, 83 

Reticular  Tissue, 83 


X  CONTEXTS. 

PAGE 

Lymphatic  Tissue,        84 

Technic  for  Reticular  and  Lymphatic  Tissue, 85 

Fat  Tissue, 85 

Technic, 89 

Cartilage,       89 

Hj^aline, 90 

Elastic, 91 

Fibrous, 91 

Technic, 92 

Bone  Tissue, 92 

Technic, 94 

Xeuroglia, 94 

CHAPTER    IV. 

The  Blood, 95 

Red  Blood  Cells,       95 

White  Blood  Cells,       96 

Blood  Platelets, 98 

Blood  Dust,       99 

Development,        99 

Technic, 100 

CHAPTER    V. 

Muscle  Tissue,        loi 

Involuntary  Smooth  Muscle, loi 

Voluntary  Striated  Muscle, 102 

Involuntary  Striated  Muscle, 106 

Development  of  Muscle  Tissue 108 

Technic, 109 

CHAPTER    VI. 

Nerve  Tissue, iii 

The  Neurone, m 

General  Structure,        iii 

The  Cell  Body, 1 1 1 

The  Nucleus, 112 

The  Cytoplasm, 112 

Neurofibrils,      113 

Perifibrillar  Substance, 113 

Chromophilic  Bodies,       113 

The  Dendrites,  116 

The  Axone,        116 

Non-medullated  Axones  (Non-meduUated  Nerve  Fibres),     .    .    .    117 

Medullated  Axones  (MeduUated  Nerve  Fibres), 117 

Theorie.";  as  to  Physiology  of  the  Neurone 121 

Significance  of  Degenerative  Changes  in  the  Neurone, 122 

Neuroglia, 125 

Technic, 127 

General  References, 127 


CONTEXTS.  XI 

PART  IV.— THE  ORGANS. 

CHAPTER    I. 

PAGE 

The  Circulatory  System, 131 

The  Blood-vessel  System, '. 131 

General  Structure 131 

Capillaries, 131 

Arteries, 133 

Veins, 137 

Technic, 139 

The  Heart, 140 

Technic, 142 

Development  of  the  Circulatory  System, 142 

The  Lymph-vessel  System, 143 

Lymph  Capillaries, 144 

Lymph  Spaces, 144 

Serous  Membranes,       144 

Technic, 145 

The  Carotid  Gland, 146 

The  Coccygeal  Gland, 146 

Technic, 146 

General  References  on  Circulatory  System, 146 

CHAPTER    n. 

Lymphatic  Organs,        147 

The  Lymph  Nodes, 147 

Technic, 150 

Haemolymph  Nodes,         151 

Technic 153 

The  Thymus, 153 

Technic, 155 

The  Tonsils,       155 

The  Palatine  Tonsils, 155 

The  Lingual  Tonsils, 157 

The  Pharyngeal  Tonsils, 157 

Technic, 158 

The  Spleen,        15S 

Technic, 163 

General  References, 163 

CHAPTER    III. 

The  Skeletal  Syste.m, 164 

The  Bones, 164 

Bone  Marrow, 168 

Red  Marrow 168 

Yellow  Marrow 170 


CONTENTS. 

PAGE 

Technic 171 

Development  of  Bone,         172 

Intramembranous  Development, 172 

Intracartilaginous  Development 175 

Subperiosteal, 177 

Growth  of  Bone 179 

Technic, 179 

The  Cartilages, 180 

Articulations, 180 

Technic, 181 

General  References 182 


CHAPTER    IV. 

The  Muscular  System. 

A  Voluntary  Muscle, 183 

Tendons, 184 

Tendon  Sheaths  and  Bursse, 184 

Growth  of  Muscle, 184 

Technic, 185 

CHAPTER    V. 

Glands  and  the  General  Structure  of  Mucous  Membranes   ....  186 

Glands — General  Structure  and  Classification 186 

Tubular  Glands 188 

Alveolar  Glands,       190 

General  Structure  of  Mucous  Membranes, 191 

CHAPTER    VL 

The  Digestive  System, 192 

Anatomical  Divisions, 192 

The  Headgut,        193 

The  Mouth,        193 

The  Mucous  Membrane  of  the  Mouth,       193 

Glands  of  the  Oral  Mucosa, 193 

Technic, 196 

The  Tongue, 196 

Technic, 200 

The  Teeth 200 

Development  of  the  Teeth, 206 

Technic, 2x2 

The  Pharynx, 212 

Technic, 213 

The  Foregut, 213 

The  CEsophagus 213 

Technic, 215 

General  Structure  of  the  Walls  of  the  (Jastro-intestinal  Canal,    .  215 


CONTENTS.  xm 

PAGE 

The  Stomach,        217 

Technic,         223 

The  Midgut,      223 

The  Small  Intestine, 223 

Peyer's  Patches, 22S 

The  Endgut, 231 

The  Large  Intestine, 231 

The  Vermiform  Appendix, 232 

The  Rectum, 234 

The  Peritoneum,  Mesentery,  and  Omentum,       235 

Blood-vessels  of  the  Stomach  and  Intestines, 236 

Lymphatics  of  the  Stomach  and  Intestine, 237 

Nerves  of  the  Stomach  and  Intestine, 23 8 

Secretion  and  the  Absorption  of  Fat, 239 

Technic, 241 

The  Larger  Glands  of  the  Digestive  System, 242 

The  Salivary  Glands, 242 

The  Parotid, 243 

The  Sublingual, 243 

The  Submaxillary, 244 

Technic, 247 

The  Pancreas, 247 

Technic, 252 

The  Liver, 253 

Excretory  Ducts  of  the  Liver, 260 

The  Gall-bladder, 261 

Technic 261 

Development  of  the  Digestive  System, 262 

General  References, 263 


CHAPTER    VII. 

The  Respir.\tory  System, 264 

The  Nares, 264 

The  Larynx, 266 

The  Trachea, 266 

Technic, 269 

The  Bronchi, 269 

The  Lungs, 273 

Development  of  the  Respiratory  System 279 

Technic, 2  So 

The  Thyreoid,       2S0 

The  Parathyreoids 283 

Technic, 2S5 

General  References, 285 

CHAPTER    VIII. 

The  Urinary  System, 286 

The  Kidney,  2S6 


COx\TEXTS. 

PAGE 

The  Kidney  Pelvis  and  Ureter,      297 

The  Urinary  Bladder, 298 

The  Suprarenal  Gland, 299 

Technic, 302 

General  References, 302 


CHAPTER    IX. 

The  Reproductive  System 303 

Male  Organs, 303 

The  Testis, 303 

The  Seminal  Ducts, 309 

The  Epididymis, 309 

The  Vas  Deferens,        310 

The  Seminal  Vesicles  and  Ejaculatory  Ducts, 311 

Rudimentary  Structures  Connected   with   the    Development     of 

the  Genital  System, 311 

The  Spermatozoon, 313 

Development  of  the  Spermatozoon, 314 

Technic, 316 

The  Prostate  Gland, 317 

Cowper's  Glands, 319 

Technic 319 

The  Penis, 319 

The  Urethra, 319 

Technic, 321 

Female  Organs, 322 

The  Ovary, 323 

The  Graafian  Follicle, 324 

The  Corpus  Luteum, 329 

The  Oviduct, 334 

Technic, 335 

The  Uterus, 336 

The  Mucosa  of  the  Resting  Uterus,       337 

The  Mucosa  of  the  Menstruating  Uterus, 338 

The  Mucosa  of  the  Pregnant  Uterus, 340 

The  Placenta 341 

The  Vagina,       345 

Development  of  the  Urinary  and  Re]jroductive  Systems 346 

Technic, 349 

General  References, 3  5° 


CHAPTER    X. 

The  Skin  and  its  Ai'pendages, 351 

The  Skin, 35^ 

Technic, 3  55 

The  Nails, 3S(> 

Technic, 3  5^ 


CONTEXTS.  XV 

PAGE 

The  Hair, 35S 

Technic, 364 

Development  of  Skin,  Nails,  and  Hair 366 

The  Mammary  Gland, 368 

Technic, 371 

General  References, 372 


CHAPTER    XL 

The  Nervous  System, 373 

Histological  Development  and  General  Structure, 373 

Membranes  of  the  Brain  and  Cord 378 

Technic, 380 

The  Peripheral  Nerves,        380 

Technic, 382 

The  Afferent  Peripheral  Neurones, 382 

The  Cerebro-spinal  Ganglia,       382 

The  Peripheral  Processes  of  the  Cerebro-spinal  Ganglion  Cells,    3S5 
The  Central  Processes  of  the  Cerebro-spinal  Ganglion  Cells,  .    390 

The  Sympathetic  Ganglia, 390 

Technic 394 

The  Efferent  Peripheral  Cerebro-spinal  Neurones ^q^ 

The  Spinal  Cord,      396 

Origin  of  the  Fibres  which  make  up  the  White  Matter  of  the  Cord,   396 
(i)    The  Spinal  Ganglion  Cell  and  the  Origin  of  the  Posterior 
Columns, 397 

(2)  Cells    Situated  in  Other  Parts  of  the  Central   Nervous 
System  which  Contribute  Axones  to  the  White    Columns 

of  the  Cord, 397 

(3)  Root  Cells — Motor  Cells  of  the  Anterior  Horn,    ....    398 

(4)  Column  Cells, 398 

(5)  Cells  of  Golgi  Type  II, 399 

Technic, 399 

Practical  Stud}^ 400 

General  Topography  of  the  Cord,  Cell  Groupings,  Arrangement  of 

Fibres  and  Finer  Structure,) 401 

Practical  Study  of  Sections  through    Lumbar  Enlargement,  401 

General  Topography,       401 

Cell  Groupings, 403 

Arrangement  of  Fibres,       405 

Finer  Structure, 405 

Blood-vessels,       406 

Variations  in  Structure  at  Different  Levels 407 

Practical  Study, 40S 

Section  through  the  Twelfth  Thoracic  Segment.     .     .     .  408 

Section  through  the  Mid-thoracic  Region,       408 

Section  through  the  Cervical  Enlargement 408 

Fibre  Tracts  of  the  Cord 408 

Ascending  Tracts 413 

I.    Long  Ascending  Arms  of  Dorsal  Root  Filires,     .     .413 


CONTENTS. 

PAGE 

II.   Spino-thalamic  Tract, 414 

III.  Dorsal  Spino-cerebellar  Tract,       415 

IV.  Ventral  Spino-cerebellar  Tract 415 

Descending  Tracts 416 

I.  The  Pyramidal  Tracts, 416 

II.  The  Tecto-spinal  Tract, 217 

III.  The  Tract  from  the  Interstitial  Nucleus  of  Cajal,   417 

IV.  The  Rubro-spinal  Tract, 417 

V.  Tracts  from  Deiters'  Nucleus, 418 

VI.   The  Fasciculus  of  Thomas, 418 

VII.    Helweg's  Tract, 418 

VIII.   The  Septo-marginal  Tract, 418 

IX.   The  Comma  Tract  of  Schultze, 419 

Fundamental  Columns  or  Ground  Bundles, 419 

A  Two-neurone  Spinal  Reflex  Arc,   .    .     .  - 420 

A  Three-neurone  Spinal  Reflex  Arc, 421 

A  Cerebellar  Arc, 421 

A  Cerebral  or  Pallial  Arc, 421 

Technic, .421 

The  Brain, 424 

General  Structure, 424 

Segmental  Brain  and  Nerves, 425 

Suprasegmental  Structures, 427 

The  Hindbrain  or  Rhombencephalon, 429 

The  Medulla  Oblongata  or  Bulb, 429 

The  Pons, 431 

The  Cerebellum  (also  p.  455), 431 

Technic, 431 

Practical  Study, 43 1 

1.  Transverse  Section  of  the  Medulla  through  the 
Decussation  of  the  Pyramidal  Tracts  (Motor  Decus- 
sation),       431 

2.  Transverse  Section  of  the  Medulla  through  the 
Decussation  of  the  Fillet  or  Lemniscus  (Sensory 
Decussation), 43. S 

3.  Transverse  Section  of  the  Medulla  through  the 
Lower  Part  of  the  Inferior  Olivary  Nucleus,      .     .     .43  7 

4.  Transverse  Section  of  the  Medulla  through  the 
Middle  of  the  Olivary  Nucleus, 439 

5.  Transverse  Section  of  the  Medulla  through  the 
Entrance  of  the  Cochlear  Root  of  Nerve  VIII,  .    .    .    439 

6.  Section  through  the  Hindbrain  at  Level  of  Junction 
of  Pons  and  Cerebellum  and  Entrance  of  Vestibular 
Nerve, 44  7 

7.  Transverse  Section  of  tlic  Hindln-ain  through  the 
Roots  of  Nerves  VI  (Abducens)  and  VII  (Facial),    .    4S° 

8.  Transverse  Section  of  the  Hindbrain  through  the 
Roots  of  Nerve  V  (Trigeminus) 452 

Tlic  Cereljcllum,       455 

The  Cerebellar  Cortex, 455 

The  Isthmus 462 


CONTENTS.  XVll 

PAGE 

Practical  Study, 462 

9.   Transverse    Section    through    the    Isthmus    at    the 

Exit  of  Nerve  IV  (Trochlearis) , 462 

The   Midbrain  or  Mesencephalon, 464 

Practical  Study,        465 

10.  Transverse    Section   through   Midbrain  at  Level   of 
Anterior  Corpora   Quadrigemina  and  Exit  of  Nerve 

III  (Oculomotor), 465 

The  Forebrain  or  Prosencephalon, 468 

The  Interbrain  (Diencephalon  or  Thalamencephalon),      .     .    468 
Practical  Study,        470 

11.  Transverse   Section    through  the  Junction   of 
Midbrain  and  Thalamus 470 

12.  Section  through  the  Interbrain  at  the    Level 

of  the  Optic  Chiasma, 472 

The  Endbrain  or  Telencephalon, 477 

The  Rhinencephalon,       477 

The  Corpus  Striatum, 478 

The  Pallium, 478 

Practical  Study, 481 

13.  Transverse     Section      through     the     Cerebral 
Hemispheres,  Corpora  Striata  and  Thalamus,     .  481 

The  Cerebral  Cortex,        481 

Technic, 488 

The  Pituitary  Body, 489 

The  Pineal  Body, 490 

Technic, 490 

Table  of  Cranial  and  Spinal  Nerves, 492 

General  Reference  for  Further  Study, 491 

CHAPTER    XII. 

The  Organs  of  Special  Sense,       494 

The  Organ  of  Vision,       494 

The  Eyeball, 494 

The  Cornea, 494 

The  Chorioid, 49.6 

The  Ciliary  Body  , 498 

The  Iris, 500 

The  Retina, 501 

The  Optic  Nerve, 505 

The  Relations  of  Optic  Nerve  to  Retina  and  Brain 506 

The  Lens,  510 

The  Lacrymal  Apparatus 512 

The  Eyelid 513 

Development  of  the  Eye 515 

Technic, 517 

The  Organ  of  Hearing 518 

The  External  Ear 51S 

The  Middle  Ear,        519 


xviii  CONTENTS. 

PAGE 

The  Internal  Ear, 520 

The  Vestibule  and  Semicircular  Canals,       520 

The  Saccule  and  Utricle, 521 

The  Semicircular  Canals, 522 

The  Cochlea 522 

Development  of  the  Ear, 529 

Technic, 529 

The  Organ  of  Smell, 530 

Technic, 532 

The  Organ  of  Taste, 532 

Technic, 533 

General  References 533 

Index, 535 


PART  I. 
HISTOLOGICAL   TECHNIC. 


CHAPTER  I. 
GENERAL  TECHNIC. 

Certain  body  fluids,  e.g.,  blood,  urine,  etc.,  may  be  examined  by 
simply  placing  them  on  a  slide  under  a  cover  glass.  A  few  tissues, 
e.g.,  thin  membranes,  such  as  the  omentum  and  the  mesentery,  may 
be  examined  fresh  in  some  such  inert  medium  as  blood  serum  or 
normal  salt  solution  (o.  75-per-cent.  aqueous  solution  sodium  chlorid). 
For  such  examination  the  tissue  is  immersed  in  the  salt  solution  on  a 
slide  and  covered  with  a  cover-glass.  Most  tissues  and  organs,  how- 
ever, require  much  more  elaborate  preparation  to  render  them  suitable 
for  microscopic  examination.  Tissues  too  dense  and  thick  to  be 
readily  seen  through  with  the  microscope  must  be  so  treated  as  to  make 
them  transparent.  This  is  accomplished  either  by  pulling  the  tissue 
apart  into  fine  shreds,  teasing,  or  by  cutting  it  into  thin  slices,  sec- 
tion cutting.  Some  tissues  admit  of  teasing  in  a  fresh  condition; 
others  can  be  satisfactorily  teased  only  after  they  have  been  subjected 
to  the  action  of  a  chemical  w^hich  breaks  down  the  substance  holding 
the  tissue  elements  together,  jnaceration.  Fresh  tissue  can  rarely  be 
cut  into  sections  sufficiently  thin  for  microscopic  examination.  It 
must  first  be  treated  in  such  a  manner  as  to  preserve  as  nearly  as  pos- 
sible the  living  tissue  relations,  fixation.  If  too  soft  for  section  cutting 
it  must  next  be  put  through  a  process  known  as  hardening.  If,  how- 
ever, as  in  the  case  of  bone,  the  tissue  is  too  hard,  it  must  be  soft- 
ened by  dissoh'ing  out  the  mineral  salts,  decalcification.  If  very  thin 
sections  are  to  be  cut,  it  is  further  necessary  to  impregnate  the  tissue 
with  some  fluid  substance  which  will  harden  in  the  tissue  and  give 
to  the  mass  a  firm,  even  consistency.     This  is  known  as  embedding. 

Furthermore,  most  tissue  elements  have  refractive  indices  which 
are  so  similar  that  their  differentiation  under  the  microscope  is  often 
extremely  difficult.  To  overcome  this  difficulty,  recourse  is  had  to 
staining  the  tissue  with  dyes  which  have  an  aflinity  for  certain  only  of 
the  tissue  elements,  or  which  stain  dift'erent  elements  with  dift'erent 
degrees  of  intensity.     This  is  known  as  differential  or  selective  staining. 

3 


4  HISTOLOGICAL  TECHNIC. 

The  final  step  in  the  process  is  the  mounting  of  the  specimen, 
after  which  it  is  ready  for  microscopic  study. 

Only  the  more  common  procedures  used  in  the  preparation  of 
tissues  for  microscopic  study  are  described  in  this  section.  At  the 
end  of  each  section  are  given  the  technical  methods  most  satisfactory 
for  the  demonstration  of  the  tissues  described  in  that  section.  For 
other  methods  the  student  is  referred  to  special  works  upon  micro- 
scopic technic. 

Dissociation  of  Tissue  Elements. 

This  method  of  preparing  tissues  for  microscopic  study  has  only 
a  limited  application,  most  specimens  being  preferably  fixed,  and 
cut  into  thin  sections.  Certain  of  the  structural  features  of  such 
tissues  as  nerves,  muscle,  and  epithelium,  which  have  but  little  inter- 
cellular substance  may  be  well  demonstrated  by  dissociation. 

This  is  accomplished  by  (i)  teasing,  or  (2)  maceration,  or  both. 

(i)  Teasing. — This  consists  in  pulling  apart  fresh  or  preserved 
tissues  by  means  of  teasing  needles.  Instructive  specimens  of  such 
tissues  as  muscle  and  nerve  may  be  obtained  in  this  way. 

(2)  Maceration. — This  is  the  subjecting  of  a  tissue  to  the  action 
of  some  chemical  which  breaks  down  the  substance  uniting  the  tissue 
elements,  thus  allowing  them  either  to  fall  apart  or  to  be  more  easily 
dissociated  by  teasing.  The  most  commonly  used  macerating  fluids 
are: 

(a)  Ranvier^s  Alcohol  (33-per-cent.,  made  by  adding  35  c.c.  of 
96-per-cent.  alcohol  to  65  c.c.  of  water). — Bits  of  fresh  tissue  are 
placed  in  this  fluid  for  from  twenty-four  to  forty-eight  hours.  The 
cells  may  then  be  easily  separated  by  shaking  or  by  teasing.  Ran- 
vier's  alcohol  is  an  especially  satisfactory  macerating  fluid  for  epithelia. 

{h)  Formaldehyde,  in  very  dilute  solutions  (0.2-  to  0.4-per-cent. 
commercial  formalin^). — Tissues  should  remain  in  the  formaldehyde 
solution  from  twenty-four  to  forty-eight  hours.  This  is  also  es- 
pecially useful  for  dissociating  epithelial  cells. 

(c)  Sodium  or  Potassium  Hydrate  (30-  to  35-per-cent.  aqueous 
solution). — From  twenty  minutes  to  an  hour  is  usually  sufficient  to 
cause  the  tissue  elements  to  fall  apart  or  to  be  readily  pulled  apart 
with  the  teasing  needles.  If  it  is  at  any  time  desirable  to  stop  the 
action  of  the  caustic  alkali,  this  may  be  accomplished  by  neutralizing 

*  Commerical  formalin  is  a  40-per-cent.  solution  of  formaldehyde  gas  in  water. 


GENERAL  TECHNIC.  5 

with  glacial  acetic  acid  or  by  replacing  the  alkali  with  a  6o-per-cent. 
aqueous  solution  of  potassium  acetate.  The  specimens  may  then  be 
preserved  in  the  potassium-acetate  solution,  in  glycerin,  or  in  50-per- 
cent, alcohol.  This  dissociating  fluid  is  largely  used  for  muscle  cells 
and  fibres. 

{d)  Nitric  acid  (10-  to  20-per-cent.  aqueous  solution). — This  is 
especially  useful  for  dissociating  involuntary  and  voluntary  muscle. 

After  any  of  the  above  procedures,  the  macerating  fluid  containing 
the  tissue  elements  should  be  placed  in  a  long  tube,  allowed  to  stand 
for  a  time  and  the  fluid  decanted.  Water  is  then  poured  into  the  tube, 
the  tissues  allowed  to  settle  and  the  water  poured  off,  this  being  re- 
peated until  all  trace  of  macerating  fluid  is  removed.  The  tissue 
elements  may  then  be  preserved  or  mounted  in  glycerin  or  in  glycerin 
Jelly.  It  is  frequently  advisable  to  stain  the  tissues.  For  this  purpose 
alum-carmin  (p.  17)  is  especially  satisfactory.  (For  details  see  technic 
I,  p.  109  and  technic  2,  p.  109).  After  staining  and  washing,  the  tissues 
may  be  preserved  or  mounted  in  glycerin,  eosin  glycerin,  or  glycerin 
jelly.  It  frequently  happens  that  on  examining  dissociated  tissue 
elements  after  mounting,  the  bits  of  tissue  are  stiU  too  large.  This 
may  be  remedied  by  gently  tapping  on  the  cover-glass  with  a  lead 
pencil. 

PREPARATION  OF  SECTIONS. 

I.  Fixation. 

Fixation  is  the  first  step  in  the  preparation  of  sections  of  tissues 
for  microscopic  study.  Its  object  is  to  so  preserve  the  tissues  that  they 
retain  as  nearly  as  possible  the  same  structure  and  relation  which  they 
had  during  life.  Fixation  of  such  a  thin  film  of  tissue  as  a  blood  smear 
may  be  accomplished  by  heating.  A  blood  smear  or  even  small  pieces 
of  tissue  may  be  fixed  by  exposure  to  certain  chemical  vapors  as,  e.g., 
the  vapor  of  formalin  or  of  osmic  acid.  Fixation  is,  however,  usually 
accomplished  by  means  of  chemicals  in  solution,  the  solution  being 
known  as  a  fixing  agent  or  fixative.  Pieces  of  tissue  are  immersed  in 
the  fixative  and  allowed  to  remain  there  until  fixation  is  complete. 
The  length  of  time  required  depends  upon  the  character  of  the  tissue 
and  upon  the  fixative  used.  The  pieces  of  tissue  should  be  small, 
and  large  quantities  of  the  fixative  should  be  used.  It  may  be  neces- 
sary to  change  the  fluid  a  number  of  times,  in  order  to  keep  it  up  to 
the  proper  strength. 


6  HISTOLOGICAL  TECHXIC. 

Organs  and  even  bodies  may  be  fixed  in  toto  by  injecting  the  fixa- 
tive through  an  artery  and  allowing  it  to  escape  through  the  veins. 
After  the  injection,  the  whole  specimen  should  be  placed  in  a  large 
quantity  of  the  same  fixative.  This  method  fills  the  entire  vascular 
system  including  the  capillaries  with  the  fixative,  thus  bringing  the 
latter  into  very  prompt  and  close  contact  with  the  tissue  elements. 
The  result  is  a  very  rapid  and  accurate  fixation  which  is  especially 
valuable  where  it  is  necessary  to  preserve  the  topographic  relations  of 
various  parts  of  an  organ  or  a  body. 

A  mercuric  chlorid  solution  (p.  7)  followed  immediately  by  strong 
alcohol  makes  a  very  good  injection  fixative.  Satisfactory  fixation  is 
largely  dependent  upon  the  freshness  of  the  tissue  when  placed  in  the 
fixative.     The  following  are  the  fixatives  in  most  common  use: 

(i)  Strong  Alcohol  (96-per-cent.). — This  is  a  rapid  fixative  and 
should  be  used  on  small  pieces  of  tissue.  The  time  required  is  from 
six  to  twenty-four  hours,  though  tissues  may  remain  longer  without 
injury.  The  alcohol  should  be  changed  after  two  or  three  hours.  This 
fixative  should  not  be  used  where  fine  histological  detail  is  desired, 
since  it  causes  some  shrinkage.  One  advantage  in  its  use  is  the  fact 
that  tissues  are  hardened  and  ready  for  embedding  at  the  end  of 
fixation. 

(2)  Dilute  Alcohol  (30-per-cent.  to  80-per-cent.). — This,  as  a  rule, 
gives  unsatisfactory  results,  causing  much  shrinkage  of  the  tissue 
elements. 

(3)  Formaldehyde  (2-per-cent.  to  lo-per-cent.  aqueous  solution). — 
Formalin  is  rapid  in  its  action  and  probably  has  better  penetrating 
qualities  than  any  other  fixative.  For  general  purposes  a  4-per-cent. 
solution  (i  part  commercial  formalin  to  9  parts  water)  should  be  used. 
This  fixes  in  from  six  to  twenty-four  hours.  The  results  after  formal- 
dehyde are  not  always  good,  owing  to  the  fact  that  it  has  little  harden- 
ing power,  and  the  subsequent  action  of  alcohol  is  Hkely  to  cause  some 
distortion  of  the  tissues.  It  acts  better  when  combined  with  other 
fixatives  than  when  used  alone.     (See  Orth's  fluid.) 

(4)  Mailer's  Fluid. 

Potassium  bichromate,  2.5  gm. 

Sodium  sulphate,  i.ogm. 

Water,  loo.o  c.c. 

This  fluid  gives  very  good  results,  but  is  extremely  slow  in  its  action, 
requiring  from  a  week  to  several  months.     Fairly  large  pieces  of  tis- 


GENERAL  TECHXIC.  7 

sue  may  be  fixed,  but  in  all  cases  large  quantities  of  the  fixative  should 
be  used  and  frequently  renewed. 

(5)  Orth's  Fluid. 

]\Iuller's  fluid  (double  strength),  \  _ 

„,,,,„  )  Equal  parts, 

rormaldehyde,  8-per-cent.,  J 

This  is  one  of  the  best  general  fixatives.  Its  action  is  similar  to  that 
of  Muller's  fluid  but  much  more  rapid,  fixation  being  accomplished 
in  from  twenty-four  to  forty-eight  hours,  though  specimens  may  remain 
in  the  fluid  several  days  without  disadvantage.  Fairly  large  pieces  of 
tissue  may  be  fixed  with  good  results.  The  fixative  should  be  changed 
after  a  few  hours.  Fixation  with  Orth's  fluid  gives  an  excellent  basis 
for  a  haematoxylin-eosin  stain  (see  (i),  p.  18.)  The  fixative  should 
always  be  freshly  prepared.  It  is  convenient  to  keep  the  8-per-cent. 
formaldehyde  solution  and  the  double-strength  Muller's  fluid  in  stock. 
Orth's  fluid  is  then  prepared  by  simply  taking  equal  parts  of  each. 

(6)  Osmic  Acid. — This,  in  a  i-per-cent.  aqueous  solution,  is  a 
quick  and  excellent  fixative  of  poor  penetrating  power.  Xtry  small 
pieces  of  tissue  must  therefore  be  used.  They  should  remain  in  the 
fluid  from  twelve  to  twenty-four  hours.  Osmic  acid  stains  fat  and 
myelin  black  and  is  consequently  useful  in  demonstrating  their  pres- 
ence in  tissues.     Fixation  should  take  place  in  the  dark. 

(7)  Flemming' s  Fluid. 

Chromic  acid,  i-per-cent.  aqueous  solution,  25  c.c. 

Osmic  acid,  i-per-cent.  aqueous  solution,  10  c.c. 

Glacial  acetic  acid,  i-per-cent.  aqueous  solution,  10  c.c. 

Water,  55  c.c. 

Flemming's  fluid  is  one  of  the  best  fixatives  for  nuclear  struc- 
tures, and  is  of  especial  value  in  demonstrating  mitotic  figures.  \'ery 
small  pieces  of  tissue  should  be  placed  in  the  fixative,  where  they 
remain  for  from  twenty-four  hours  to  three  days.  The  solution  should 
be  freshly  made  as  required,  or  a  stock  solution  without  the  osmic 
acid  may  be  kept,  and  the  latter  added  at  the  time  of  using. 

(8)  Mercuric  Chlorid. — This  may  be  used  either  in  saturated 
aqueous  solution  or  in  saturated  solution  in  o.  75-per-cent.  salt  solu- 
tion. Fixation  is  complete  in  from  twelve  to  twenty-four  hours,  and 
is  usually  very  satisfactory. 

A  saturated  solution  of  mercuric  chlorid  in  5-per-cent.  aqueous 
solution  of  glacial  acetic  acid  also  wives  good  results. 


8  HISTOLOGICAL  TECHNIC.     . 

(9)  Zenker'' s  Fluid. 

Potassium  bichromate,  2  . 5  gm. 

Sodium  sulphate,  i.ogm. 

Mercuric  chlorid,  5  .  o  gm. 

Glacial  acetic  acid,  5.0  c.c. 

Water,  100. o  c.c. 

This  fluid  should  be  freshly  made,  or  the  salts  may  be  kept  in  solu- 
tion and  the  acetic  acid  added  at  time  of  using. 

Zenker's  fluid  is  a  good  general  fixative,  but  usually  causes  some 
shrinkage  of  the  tissue  elements.  Fixation  requires  from  six  to  twenty- 
four  hours.  The  most  serious  drawback  to  Zenker's  fluid  is  the  fact 
that  the  mercuric  chlorid  sometimes  produces  dark,  irregular  precip- 
itates in  the  tissues.  This  may  be  remedied,  however,  by  the  use  of 
iodine  and  iodid  of  potassium  in  the  hardening  process  (see  Harden- 
ing, p.  9). 

(10)  Picric  acid  is  an  excellent  fixative  for  cytoplasm.  It  may  be 
used  in:  {a)  Saturated  aqueous  solution;  (b)  saturated  solution  of 
picric  acid  in  i-per-cent.  aqueous  solution  of  acetic  acid;  (c)  saturated 
solution  of  picric  acid  in  2-per-cent.  aqueous  solution  of  sulphuric 
acid. 

II.  Hardening. 

Most  fixatives  are  also  hardening  agents  if  their  action  is  prolonged. 
This  is,  however,  often  detrimental.  It  is,  therefore,  customary,  after 
fixation  is  complete,  to  carry  the  specimens,  with  or  without  washing, 
through  successively  stronger  grades  of  alcohol  for  the  purpose  of 
hardening  the  tissues.  For  general  histological  purposes  the  specimens 
may  be  transferred  directly  to  70-per-cent.  or  80-per-cent.  alcohol, 
which  should  be  changed  once  or  twice.  In  the  case  of  delicate  tissues 
the  first  grade  of  alcohol  should  be  40-per-cent.  or  50-per-cent.,  the 
second  70-per-cent.,  and  the  third  80-per-cent.  The  specimens  should 
remain  in  each  grade  from  twelve  to  twenty-four  hours. 

Washing  the  tissues  after  fixation  is  not  a  matter  of  indifference. 
In  some  cases  water  should  be  used,  while  in  other  cases  water  is  liable 
to  undo  the  action  of  the  fixative,  in  which  cases  alcohol  must  be  used 
for  washing. 

After  fixation  in  alcohol  no  washing,  of  course,  is  necessary.  Speci- 
mens fixed  in  strong  alcohol  are  embedded  immediately  (see  Embed- 
ding, p.  to),  or  preserved  (see  Preserving,  p.  9).     After  fixation  in  dilute 


GENERAL  TECHNIC.  9 

alcohol  the  specimens  are  passed  through  the  graded  alcohols  up  to 
8o-per-cent. 

After  fixation  in  formaldehyde  solutions  the  specimens  are  passed 
directly  through  the  graded  alcohols  without  washing  in  water.  Speci- 
mens fixed  in  any  solution  containing  picric  acid  should  not  be 
washed  in  water,  but  passed  directly  through  the  alcohols;  and  it  is 
usually  necessary  to  change  each  grade  in  order  to  wash  out  the  picric 
acid. 

Specimens  fixed  in  osmic  acid  or  any  solution  containing  osmic 
acid  should  be  washed  in  running  water  before  being  passed  through 
the  graded  alcohols.  After  solutions  containing  potassium  bichro- 
mate the  specimens  should  be  washed  in  water  suflficiently  to  remove 
the  excess  of  bichromate,  though  too  prolonged  washing  seems  to  be 
detrimental.  A  precipitate  forms  in  the  alcohols,  but  this  apparently 
does  no  harm. 

After  mercuric  chlorid  or  Zenker  fixation  the  washing  may  be  done 
either  in  water  or  in  alcohol.  To  avoid  precipitates  in  the  tissues  add 
a  small  quantity  of  an  iodin  solution  (equal  parts  tincture  iodin  and 
lo-per-cent.  aqueous  solution  potassium  iodid)  to  any  of  the  grades  of 
alcohol.  As  the  alcohol  becomes  clear  more  of  the  solution  is  added 
until  the  alcohol  remains  slightly  tinged. 

III.  Preserving. 

Hardened  tissues  are  usually  preserved  in  8o-per-cent.  alcohol. 
Formalin  in  aqueous  solutions  of  i-per-cent.  to  lo-per-cent.  is  also 
used  as  a  preservative.  In  either  case,  when  it  is  necessary  to  pre- 
serve the  specimens  for  a  considerable  length  of  time  (several  months 
or  longer),  the  tissues  are  likely  to  lose  their  staining  qualities  to  a 
certain  extent.  Preserving  the  specimens  in  equal  parts  of  strong 
alcohol,  glycerin,  and  distilled  water  is  successful  as  a  partial  remedy 
for  this. 

IV.  Decalcifying. 

Tissues  containing  lime  salts,  like  bones  and  teeth,  must  have 
the  lime  salts  dissolved  out  before  sections  can  be  cut.  This  process 
is  known  as  decalcification. 

Tissues  to  be  decalcified  must  be  first  fixed  and  hardened.  Fix- 
ation in  Orth's  fluid  and  hardening  in  graded  alcohols  gi\'e  good  results. 
After  hardening,  the  tissue  is  washed  in  water  and  placed  in  one  of  the 


10  HISTOLOGICAL  TECHNIC. 

following  decalcifying  fluids.  The  quantity  of  fluid  should  always  be 
large  and  the  fluid  frequently  changed.  The  completion  of  decalcifi- 
cation can  be  determined  by  passing  a  needle  through  the  specimen 
or  by  cutting  it  with  a  scalpel.  The  time  required  varies  with  the 
size  and  hardness  of  the  specimen  and  the  decalcifying  fluid  used. 

(i)  Hydrochloric  Acid. — This  may  be  used  in  aqueous  solutions 
of  from  o.  5-per-cent.  to  5-per-cent.  A  very  satisfactory  decalcifying 
mixture  is  that  known  as  Ebner's  hydrochloric-salt  solution.  It  con- 
sists of: 

Sodium  chlorid,  saturated  aqueous  solution,  i  part. 

Water,  2  parts. 

Hydrochloric  acid,  sufficient  to  make  a  from  2-per-cent.  to  S-per- 
cent.  solution. 

The  addition  of  the  salt  prevents  swelling  of  the  tissue.  This  fluid 
is  slow  in  acting  and  should  be  changed  every  day.  When  decalcifi- 
cation is  complete,  the  specimen  is  washed  in  sufficient  changes  of 
water  to  remove  all  trace  of  acid.  This  may  be  quickly  accomplished 
by  the  addition  of  a  little  ammonium  hydrate  to  the  water.  The  speci- 
men is  then  carried  through  graded  alcohols. 

(2)  Nitric  Acid. — This  is  less  used  than  the  preceding.  The 
strength  should  be  from  i-per-cent.  to  lo-per-cent.  aqueous  solution. 
Weak  solutions  (i-per-cent.  to  2-per-cent.)  wiU  decalcify  smaH  foetal 
bones  in  from  three  to  twelve  days.  For  larger  bones  stronger  solutions 
and  longer  time  are  required. 

(3)  Small  bones  may  be  satisfactorily  decalcified  in  Zenker' s  fluid 
(see  Fixatives,  page  8),  or  in  the  following: 


Picric  acid. 

I  part. 

Chromic  acid, 

I   part. 

Glacial  acetic  acid. 

V.  Embedding. 

5  parts. 

Most  hardened  tissues  are  still  not  firm  enough  to  be  cut  into  the 
thin  sections  suitable  for  microscopic  study.  In  order  to  support  the 
tissue  elements  and  render  them  more  firm  for  section  cutting,  recourse 
is  had  to  embedding.  This  consists  in  impregnating  the  tissues  with 
some  substance  which  is  hquid  when  the  tissues  are  placed  in  it,  but 
which  can  be  made  to  solidify  throughout  the  tissues.  In  this  way  the 
tissue  elements  are  held  firmly  in  place.  The  embedding  substances 
most  used  are  cefloidin  and  paraffin. 


GENERAL  TECHXIC.  11 


Celloidix  Embeddixg. 


(i)  Alcohol-ether  Celloidix. — Two  solutions  should  be  made. 

Solution  No.  2.  Thick  celloidin — a  5-per-cent.  solution  of  celloidin 
in  equal  parts  96-per-cent.  alcohol  and  ether. 

Solution  No  1.  Thin  celloidin — made  by  diluting  solution  Xo.  2 
with  an  equal  volume  of  equal  parts  of  alcohol  and  ether. 

The  hardened  tissues  are  placed  successively  in : 

Strong  alcohol  (96-per-cent.)  twelve  to  twenty-four  hours,  to  dehy- 
drate. 

Equal  parts  alcohol  and  ether,  twelve  to  twenty-four  hours. 

Thin  celloidin,  twenty-four  hours  to  several  days. 

Thick  celloidin,  twenty-four  hours  or  longer. 

The  exact  time  tissues  should  remain  in  the  different  grades  of 
celloidin  depends  upon  the  character  of  the  tissue,  the  size  of  the  speci- 
men, and  the  thinness  of  section  desired.  Many  tissues  may  be  advan- 
tageously left  for  weeks  in  thin  celloidin. 

The  specimen  must  now  be  "blocked"  and  the  celloidin  hardened. 
By  blocking  is  meant  fastening  the  specimen  impregnated  with  celloidin 
to  a  block  of  wood  or  other  suitable  material  which  may  be  clamped 
in  the  microtome  (see  Section  Cutting,  p.  13).  The  specimen  may 
be  taken  from  the  thick  celloidin  (considerable  of  the  latter  adhering  to 
the  specimen,^,  quickly  pressed  upon  a  block  of  wood  or  vulcanized 
fibre,  allowed  to  harden  five  to  ten  minutes  in  air,  and  then  immersed 
in  80-per-cent.  alcohol.  The  alcohol  gives  an  even  hardening  of  the 
celloidin,  attaching  the  specimen  firmly  to  the  block.  Another  method, 
and  one  by  which  very  even-shaped  blocks  may  be  obtained,  is  to  place 
the  specimen  from  the  thick  celloidin  into  a  little  paper  box  (made  by 
folding  paper  over  a  wooden  block),  slightly  larger  than  the  specimen, 
and  covering  with  thick  celloidin.  The  celloidin  should  dry  slowly 
under  a  bell-jar  for  from  two  to  twelve  hours,  according  to  the  amount 
of  celloidin,  after  which  it  should  be  immersed  in  80-per-cent.  alcohol 
and  the  paper  pulled  off.  Such  a  block  may  be  cut  into  any  desired 
shape.  It  is  attached  to  the  wooden  or  vulcanized  block  by  dipping 
for  a  moment  in  thick  celloidin,  and  tlien  pressing  firmly  down  upon 
the  block.  After  five  to  ten  minutes'  drying  in  air  it  is  transferred  to 
80-per-cent.  alcohol. 

Old,  hard,  celloidin-embedded  specimens  are  sometimes  difticult 
to  attach  to  blocks.  This  usually  may  be  accomplished  by  first  thor- 
oughly drying  the  specimen  and  then  dipping  it  in  equal  parts  alcohol 


12  HISTOLOGICAL  TECHNIC. 

and  ether  for  a  few  minutes.  This  softens  the  surface  of  the  celloidin, 
after  which  the  specimen  is  dipped  in  thick  celloidin  and  blocked. 
Embedded  or  blocked  specimens  can  be  kept  in  8o-per-cent.  alcohol. 
iVfter  several  months,  however,  the  celloidin  is  likely  to  become  too  soft 
for  good  section  cutting.  In  that  case  the  specimens  can  be  readily 
re-embedded  by  dissolving  out  the  old  celloidin  with  alcohol  and  ether 
and  putting  them  again  through  the  regular  embedding  process. 

(2)  Clove-oil  Celloidin. — A  more  rapid  impregnation  of  the 
tissue  may  be  obtained  by  means  of  what  is  known  as  clove-oil  cel- 
loidin. 

Celloidin,  3°  g^- 

Clove  oil,  100  c.c. 

Ether,  4°°  c.c. 

Alcohol,  absolute,  20  c.c. 

The  celloidin  is  first  placed  in  a  jar  and  the  clove  oil  and  ether  added. 
From  two  to  four  days  are  required  for  solution  of  the  celloidin.  Dur- 
ing this  time  the  jar  should  be  shaken  several  times.  After  the  celloidin 
is  dissolved  the  absolute  alcohol  is  added  and  the  solution  is  ready  for 
use. 

The  specimen  must  be  thoroughly  dehydrated,  placed  in  alcohol 
and  ether  or  pure  ether  for  a  few  hours,  and  then  transferred  to  the 
clove-oil  celloidin.  From  six  to  twelve  hours  is  sufficient  to  impreg- 
nate small  pieces  of  tissue.  The  tissue  is  now  taken  from  the  cel- 
loidin, placed  directly  upon  a  wooden  or  vulcanized  block,  and  im- 
mersed in  chloroform.  The  celloidin  hardens  in  about  an  hour,  and 
is  then  ready  for  sectioning.  The  specimen  is  very  firm,  and  very 
thin  sections  can  be  cut. 

A  disadvantage  in  clove-oil  celloidin  is  that  neither  the  blocks 
nor  the  sections  can  be  kept  permanently  in  alcohol,  as  can  those 
embedded  in  alcohol-ether  celloidin.  They  may,  however,  be  kept 
for  several  weeks  in  pure  chloroform. 

Paraffin  Embedding. 

For  paraffin  embedding  a  thermostat  or  paraffin  oven  is  necessary 
in  order  that  a  constant  temperature  may  be  maintained.  The  tem- 
perature should  be  about  56°  C.  Pure  paraffin,  the  melting-point  of 
which  is  from  50°  to  55°  C,  is  used.  In  very  warm  weather  it  may 
be  necessary  to  add  to  this  a  little  paraffin,  the  melting-point  of  which  is 
62°  C. 


GENERAL  TECHXIC  .  13 

The  hardened  tissue  is  first  put  in  96-per-cent.  alcohol  for  from 
twelve  to  twenty-four  hours,  and  then  completely  dehydrated  by  put- 
ting in  absolute  alcohol  for  the  same  length  of  time,  or  less  for  small 
specimens.  It  is  then  transferred  to  some  solvent  of  paraffin.  Some 
of  the  solvents  used  are  xylol,  oil  of  cedarwood,  chloroform,  and  toluol. 
Of  these  the  best  are  perhaps  xylol  and  oil  of  cedarwood.  The  tissue 
should  remain  in  either  of  these  for  several  hours,  or  until  the  tissue 
becomes  more  or  less  transparent.  It  is  then  placed  in  melted  par- 
affin, in  the  paraffin  oven,  for  from  one  to  three  hours,  according  to 
the  size  and  density  of  the  specimen.  This  allows  the  tissues  to 
become  impregnated  with  the  melted  paraffin.  The  paraffin  should 
be  changed  twice. 

In  case  of  very  delicate  tissues  it  is  well  to  transfer  them  from 
the  absolute  alcohol  to  a  mixture  of  equal  parts  absolute  alcohol  and 
xylol  for  a  short  time  before  putting  them  into  the  pure  xylol.  In 
the  same  way  a  mixture  of  equal  parts  xylol  and  paraffin  may  be  used 
before  putting  the  tissues  into  pure  paraffin. 

For  hardening  the  paraffin  in  and  around  the  tissue  a  very  con- 
venient apparatus  consists  of  a  plate  of  glass  and  several  L-shaped 
pieces  of  iron  or  lead.  Two  of  these  are  placed  on  the  glass  plate 
in  such  a  manner  as  to  enclose  a  space  of  the  desired  size.  Into  this 
are  placed  the  specimen  and  sufficient  melted  paraffin  to  cover  it. 
Both  glass  and  irons  should  be  smeared  with  glycerin  to  prevent  the 
paraffin  from  adhering,  and  should  be  as  cold  as  possible,  so  that  the 
paraffin  may  harden  quickly.  The  same  paper  boxes  described  under 
celloidin  embedding  may  also  be  used  for  paraffin.  Another  good 
method  for  small  pieces  of  tissue  is  to  place  the  specimen  in  paraffin 
in  an  ordinary  watch-glass  which  has  been  coated  with  glycerin. 
Both  paper-box  and  watch-glass  specimens  are  immersed  in  cold 
water  as  soon  as  the  surface  of  the  paraffin  has  become  hard.  After 
the  paraffin  has  hardened  any  excess  may  be  cut  away  with  a  knife. 

Paraffin-embedded  specimens  may  be  kept  indefinitely  in  air. 
For  section  cutting,  the  block  of  paraffin  is  attached  to  a  block  of  wood 
or  of  vulcanite  or  to  the  metallic  block-holder  of  the  microtome.  This 
is  done  by  heating  the  block-holder,  pressing  the  paraffin  block  firmly 
upon  it,  and  then  dipping  the  whole  into  cold  water. 

VI.  Section  Cutting. 

The  older  method  of  making  free-hand  sections  with  a  razor  has 
been  almost  completely  superseded  by  the  use  of  a  cutting  instru- 


14  HISTOLOGICAL  TECHXIC. 

ment  known  as  the  microtome.  This  consists  essentially  of  a  clamp 
for  holding  the  specimen  and  a  microtome  knife  or  razor.  The  two 
are  so  arranged  that  when  knife  and  specimen  meet,  a  section  of  any 
desired  thickness  may  be  cut. 

The  technic  of  section  cutting  differs  according  to  whether  the 
specimen  is  embedded  in  celloidin  or  in  paraffin. 

In  cutting  celloidin  sections  the  knife  is  so  adjusted  that  it  passes 
obliquely  through  the  specimen,  as  much  as  possible  of  the  cutting 
edge  being  used.  The  knife  is  kept  flooded  with  8o-per-cent.  alco- 
hol and  the  specimens  are  removed  by  means  of  a  camel's-hair  brush 
to  a  dish  of  8o-per-cent.  alcohol  where  they  may  be  kept  for  some 
time  if  desired.  When  celloidin  sections  tear  or  when  very  thin  sec- 
tions are  desired,  it  is  often  of  advantage  to  paint  the  surface  of  the 
block,  after  cutting  each  section,  with  a  coat  of  very  thin  celloidin. 

Celloidin  sections  are  usually  not  thinner  than  io,«,  although 
under  favorable  conditions  sections  5«^  or  even  3«  in  thickness  may 
be  obtained. 

In  cutting  parafi&n  sections  the  knife  is  kept  dry  and  is  passed 
not  obliquely  but  straight  through  the  specimen,  only  a  small  part  of 
the  cutting  edge  being  used.  An  exception  is  made  in  the  case  of 
very  large  parafi&n  sections,  where  an  oblique  knife  is  used.  Sec- 
tions are  removed  from  the  knife  by  a  dry  or  slightly  moistened  brush. 
If  not  desired  for  immediate  use  the  sections  may  be  conveniently 
kept  for  a  short  time  on  a  piece  of  smooth  paper.  If  sections  curl 
they  may  be  flattened  by  floating  on  warm  30-per-cent.  alcohol  or  on 
warm  water. 

Paraffin  sections  may  be  so  cut  that  the  edges  of  the  sections  adhere. 
Long  series  or  "ribbons"  of  sections  may  thus  be  secured.  This 
is  of  decided  advantage  when  serial  sections  are  desired.  Failure 
of  the  sections  to  cut  evenly  or  to  adhere  in  ribbons,  is  usually  due  to 
the  paraffin  being  too  hard  and  brittle,  which  of  course  is  due  to  its 
low  temperature.  If  much  section  cutting  is  to  be  done,  the  operator 
will  find  himself  amply  repaid  by  having  the  room-temperature  fairly 
high.  In  case  paraffin  of  a  melting-point  of  50°  to  55°  C.  is  used,  a 
room  temperature  of  73°  to  75°  F.  will  greatly  facilitate  the  work. 
Where  it  is  not  possible  to  have  a  high  room  temperature,  recourse 
may  be  had  to  coating  the  surface  of  the  block  with  a  paraffin  of  lower 
melting-point    than  that  used  for  the  embedding.     A  similar  effect 

'/<  =  micromillimeter  or  micron  =  xihn  "^  ^  millimeter  =  microscopic  unit  of 
measure  =  about  .,  '\-,r,  of  an  inch. 


GENERAL  TECHXIC.  15 

may  be  obtained  by  holding  a  heated  metal  plate  or  bar  near  the  block 
until  the  paraffin  is  slightly  softened.  This  process  may  be  repeated 
as  often  as  necessary. 

In  addition  to  the  fact  that  ribbon  series  can  be  cut  in  paraffin, 
this  embedding  substance  also  has  the  advantage  over  celloidin  that 
thinner  sections  can  be  obtained.  On  the  other  hand,  celloidin  em- 
bedding produces  less  shrinkage  of  the  tissues  than  paraffin  embedding 
with  the  accompanying  heat. 

VII.  Staining. 

This  is  for  the  purpose  of  more  readily  distinguishing  the  differ- 
ent tissue  elements  from  one  another  by  their  reactions  to  certain 
dyes. 

Based  upon  their  action  upon  the  different  tissue  elements,  stains 
may  be  classified  as  (i)  nuclear  dyes,  which  stain  nuclear  structures; 
and  (2)  plasma  dyes,  which  stain  the  cell  body  or  cytoplasm.  Plasma 
dyes,  also,  as  a  rule,  stain  the  intercellular  tissue  elements,  and  are 
therefore  known  as  diffuse  stains. 

The  dyes  most  frequently  used  for  staining  tissues  are: 

I.  Nuclear  dyes:  (a)  Haematoxylin  and  its  active  principle,  hasmat- 
ein;  (b)  carmine  and  its  active  principle,  carminic  acid;  (c)  basic 
aniline  dyes. 

II.  Plasma  dyes:  (a)  Eosin;  (b)  neutral  carmine,  (r)  picric  acid; 
(d)  acid  aniline  dyes. 

I.  Nuclear  Dyes. — (a)  H.^matoxylin. 

1.  Gage^s  Hematoxylin. 

Ammonia  or  potash  alum,  7.5  gm. 

Distilled  water,  200.0  c.c. 
Boil  for  10  minutes  to  sterilize;  cool  and  add  the  following 
solution: 

Haematoxylin  crystals,  o.i  gm. 

Alcohol  95-per-cent.,  10. o  c.c. 

Four  grams  chloral  hydrate  are  then  added  to  the  mixture 
to  prevent  growth  of  germs. 

This  dye  may  be  used  in  full  strength  or  diluted  with  alum  water. 
It  stains  in  from  two  to  five  minutes. 

2.  Delapehfs  HcFmatoxylin. 

Hiematoxylin  crystals,  i  gm. 

Alcohol,  6  c.c. 

Ammonia  alum,  saturated  aqueous  solution,  100  c.c. 


16  HISTOLOGICAL  TECHNTIC. 

The  hsematoxylin  should  be  first  dissolved  in  the  alcohol  and  then 
added  to  the  alum  solution.  The  mixture  should  next  be  allowed  to 
stand  in  the  light  for  from  seven  to  ten  days  to  ripen.  It  is  then  filtered, 
and  to  the  filtrate  are  added : 

Glycerin,  25   c.c. 

Wood  naphtha,  25   c.c. 

The  mixture  is  again  allowed  to  stand  for  from  two  to  four  days  and 
filtered.  It  may  be  used  full  strength  or  diluted  with  equal  parts  of 
water.     It  stains  in  from  two  to  five  minutes. 

3.  H eidenhain'' s  Hematoxylin. 

Hsematoxylin  crystals,  i  gm. 

Water,  100  c.c. 

Sections  are  first  placed  for  from  four  to  eight  hours  in  a  2.  5-per-cent. 
aqueous  solution  of  ammonium  sulphate  of  iron.  They  are  then 
washed  in  water  and  transferred  to  the  hsematoxylin  solution  until  they 
are  intensely  blue  or  black  (usually  several  hours).  The  sections  are 
now  washed  in  water  and  differentiated  by  again  placing  in  the  iron 
solution  till  they  have  a  light  grayish  color.  After  this  they  are  thor- 
oughly washed  in  water. 

4.  Mayer^s  Hcemalum. 

Haematein,  i  gm. 

Alcohol,  50  c.c. 

Ammonia  alum,  5-per-cent.  aqueous  solution,  1,000  c.c. 

The  haematein  is  first  dissolved  in  the  alcohol,  after  which  the  alum 
is  added.  This  dye  does  not  require  any  ripening,  and  is  thus  avail- 
able for  immediate  use.  It  is  a  rapid  nuclear  dye  usually  requiring 
not  more  than  from  three  to  five  minutes. 

5.  A  combination  of  Gage's  and  Mayer's  formulae  makes  a  very 
satisfactory  nuclear  dye. 


Haematein, 

5  gm- 

Alcohol, 

50  c.c. 

Chloral  hydrate. 

20  gm. 

Ammonia  alum,  5-per-cent.  aqueous  solution  (steril- 

ized), 

1,000  c.c. 

The  haematein  is  first  dissolved  in  the  alcohol  and  then  added  with 
the  chloral  hydrate  to  the  alum  solution.  This  solution  is  used  in 
full  strength  and  stains  in  from  three  to  five  minutes. 


GENERAL  TECHNIC.  17 

6.  Weigert's  HcBmatoxylin. 

Two  stock  solutions  should  be  made  up  as  follows : 

A.  i-per-cent.  haematoxylin,  in  96-per-cent.  alcohol. 

B.  Hydrochloric  acid  (sp.  gr.  1.126),  10  c.c. 
Ferric  chloride,  30-per-cent.,  40  c.c. 
Distilled  water,  950  c.c. 

For  use,  mix  equal  parts  of  A  and  B.  The  mixture  will  keep  two  or 
three  days.  This  is  a  rapid  stain  usually  requiring  not  more  than  a 
minute.  A  more  brilliant  nuclear  stain  may  be  obtained  by  over- 
staining  and  then  decolorizing.  After  the  stain  wash  the  sections  in 
water  and  then  decolorize  to  the  proper  degree  in  weakly  acidulated 
water.  To  stop  the  action  of  the  acid  the  sections  should  be  dipped  in 
water  made  slightly  alkaline  with  ammonia.  This  is  an  excellent  stain 
and  gives  brilliant  results.  It  is  especially  good  in  cases  where  the 
material  has  become  old  and  lost  its  affinity  for  ordinary  haematoxylin 
stains. 

{h)  Alum-carmine. 

Carmine,  2  gm. 

Alum,  5  gm. 

Carbolic  acid,  2  gm. 

Water,  100  c.c. 

The  alum  is  first  dissolved  in  the  100  c.c.  of  warm  distilled  water, 
after  which  the  carmine  is  added.  This  mixture  is  then  boiled  for 
twenty  minutes,  allowed  to  cool,  and  filtered.  The  carbolic  acid  is 
then  added.     This  is  a  slow-acting  pure  nuclear  dye. 

(c)  Basic  Aniline  Dyes — gentian  violet,  methyl  violet,  methyl 
green,  methyl  blue,  toluidin  blue,  fuchsin,  thionin,  safranin,  etc. 

These  are  best  kept  in  stock  in  saturated  alcoholic  solutions. 
When  desired  to  use,  a  few  drops  of  the  alcoholic  solution  are  added 
to  distilled  water.  No  rule  as  to  exact  proportions  can  be  given,  as 
these  depend  upon  the  material,  the  fixation,  and  the  intensity  of  stain 
desired. 

II.  Plasma  Dyes. — {a)  Eosin. 

This  is  prepared  as  follows:  Water-soluble  eosin  is  dissohed  in 
water  to  saturation.  It  is  then  precipitated  by  hydrochloric  acid 
and  the  precipitate  washed  with  water  upon  a  filter  until  the  filtrate 
is  tinged  with  eosin.  After  drying,  the  precipitate  is  dissolved  in 
strong  alcohol,  i  gm.  of  eosin  to  1,500  c.c.  of  alcohol.  This  is  a  rapid 
plasma  stain. 


18  HISTOLOGICAL  TECHNIC. 

(b)  NEUTILA.L  Carmine. 

Carmine,  i  gm. 

Liquor  ammonii  caustici,  5   c.c. 

Distilled  water,  50  c.c. 

The  last  two  ingredients  are  first  mixed,  and  tlie  carmine  then  added. 
This  solution  is  allowed  to  remain  in  an  open  vessel  for  about  three 
days,  or  until  the  odor  of  ammonia  has  disappeared,  after  which  it  is 
filtered. 

(c)  Picric  Acid — used  mainly  as  the  plasma-staining  element  of 
such  a  staining  mixture  as  picro-acid-fuchsin. 

(d)  Acid  Aniline  Dyes. — Of  these,  acid  fuchsin,  erythrosin,  and 
orange  G  are  most  used.  They  may  be  prepared  and  kept  in  stock 
in  the  same  manner  as  the  basic  aniline  dyes  (see  above).  Erythrosin 
is  of  especial  value  for  sections  which  take  the  eosin  stain  poorly. 

Staining  Secticns. 

It  is  often  of  advantage  to  stain  the  different  tissue  elements  dif- 
ferent colors.  This  may  be  accomplished  either  by  staining  suc- 
cessively with  several  dyes,  or  by  a  single  staining  with  a  mixture 
of  dyes.     The  following  are  the  methods  in  most  common  use: 

(i)  Staining  Double  w^ith  Hematoxylin  and  Eosin. — Sec- 
tions are  first  washed  in  water.  They  are  then  stained  with  hsema- 
toxylin  (solutions  i,  2,  4,  5,  or  6,  pp.  15-17)  from  one  to  five  min- 
utes. After  being  thoroughly  washed  in  water,  they  are  dehydrated 
in  strong  alcohol  and  transferred  to  the  alcoholic  eosin  solution  (page 
17).  Most  sections  stain  in  from  two  to  five  minutes.  By  this  method 
nuclei  are  stained  blue  or  purple,  cell  bodies  and  intercellular  substances 
red. 

Very  often  a  more  brilliant  staining  may  be  accomplished  as  fol- 
lows: Overstain  in  hasmatoxylin  and  wash  thoroughly  in  water;  de- 
colorize in  water  slightly  acidulated  (8  or  10  drops  of  hydrochloric  acid 
to  100  c.c.  of  water)  until  only  the  nuclei  retain  the  stain;  wash  in 
water  which  has  been  made  slightly  alkaline  with  ammonium  hy- 
drate; then  stain  with  eosin  as  usual. 

(2)  Staining  with  Picro-acid-euchsin. 

Acid-fuchsin,  i-per-cent.  aqueous  solution,  5   c.c. 

Picric  acid,  saturated  aqueous  solution,  100  c.c. 

This  solution  usually  stains  in  from  one  to  three  minutes.  Occa- 
sionally a  longer  staining  is  required.     Cell  bodies  including  muscle 


GENERAL  TECHXIC.  19 

cells  and  fibres  are  stained  yellow  by  the  picric  acid,  connective- 
tissue  fibres  red  by  the  fuchsin.  After  staining,  the  sections  are 
washed  in  distilled  water. 

(3)  Triple  Staining  with  H.ematoxylin  and  Picro-acid- 
FUCHSIN. — This  is  the  same  as  the  preceding  except  that  before  stain- 
ing with  picro-acid-fuchsin,  the  sections  are  overstained  in  haema- 
toxylin  (solutions  i,  2,  4,  5,  or  6,  pp.  15-17).  The  usual  purple  of 
haematoxylin-stained  nuclei  is  changed  to  brown  by  the  action  of  the 
picric  acid.  Care  should  be  taken  that  the  sections  do  not  remain 
too  long  in  the  picro-acid-fuchsin,  or  the  haematoxylin  may  be  com- 
pletely removed.  After  staining,  sections  are  washed  in  distilled 
water  and  transferred  to  96-per-cent.  alcohol. 

If  sections  overstain  with  fuchsin,  the  staining  solution  may  be 
diluted  with  water;  if  sections  are  understained  with  fuchsin,  more 
fuchsin  may  be  added.  If  the  picric-acid  stain  is  not  sufficiently 
intense,  the  96-per-cent.  alcohol  should  be  tinged  with  picric  acid. 

(4)  Staining  with  Picro-carmine. 

Ammonium  carminate,  i  gm. 

Distilled  water,  35   c.c. 

Picric  acid,  saturated  aqueous  solution,  15   c.c. 

The  ammonium  carminate  is  first  dissolved  in  the  water,  after  which 
the  saturated  aqueous  solution  of  picric  acid  is  added  with  constant 
stirring.  The  mixture  is  then  allowed  to  stand  in  an  open  vessel  for 
two  days,  when  it  is  filtered.  This  fluid  stains  nuclei  and  connective 
tissue  red,  cell  protoplasm  yellow. 

Staining  in  Bulk. 

By  this  is  meant  the  staining  of  blocks  of  tissue  before  cutting 
into  sections.  The  method  is  much  less  used  than  formerly.  It  is 
slower  than  section  staining  and  more  difficult  to  control.  Blocks  of 
the  hardened  tissue  are  transferred  to  the  stain  from  water  or  alcohol 
according  to  the  solvent  of  the  stain.  Alum-carmine  and  borax- 
carmine  are  the  most  used  general  bulk  stains. 

(i)  Alum-carmine. 

Carmine,  0.5  to  i  gm. 

Ammonia  alum,  4-per-cent.  aqueous  solution,  100   c.c. 

After  mixing  the  ingredients,  the  solution  should  be  boiled  fifteen 
minutes,  and  after  cooling,  enough  sterile  water  added  to  replace  that 
lost  by  evaporation.     The  time  reciuircd  for  staining  depends  upon 


20  HISTOLOGICAL  TECHNIC. 

the  size  of  the  specimen.     There  is,  however,  Httle  danger  of  over- 
staining.     After  washing  out  the  excess  of  stain  with  water  the  speci- 
men is  dehydrated  and  embedded  in  the  usual  way. 
(2)  Borax- CARMINE,  Alcoholic  Solution. 

Carmine,  3  gm. 

Borax,  4  gm. 

Water,  93  c.c. 

After  mixing  the  above,  add  100  c.c.  70-per-cent.  alcohol, 
allow  the  mixture  to  settle,  then  filter. 

About  twenty-four  hours  is  required  to  stain  blocks  0.5  cm.  in 
diameter.     Larger  blocks  require  longer  staining. 

VIII.  Mounting. 

It  is  usually  desirable  to  make  permanent  preparations  or  ''  mounts  " 
of  the  stained  specimens. 

The  most  satisfactory  media  for  mounting  specimens  are  glycerin 
and  Canada  balsam. 

(i)  Glycerin. — Sections  may  be  transferred  to  glycerin  from 
either  water  or  alcohol.  In  the  case  of  double-stained  specimens — 
haematoxylin-eosin — the  glycerin  should  be  tinged  with  eosin,  as  the 
pure  glycerin  abstracts  the  eosin  from  the  tissues.  In  many  cases 
satisfactory  eosin  staining  may  be  obtained  by  simply  placing  the 
haematoxylin-stained  specimens  in  glycerin  strongly  tinged  with  eosin 
(eosin-glycerin).  The  specimen  in  a  drop  of  glycerin  is  transferred 
to  the  glass  mounting  slide,  the  excess  of  glycerin  removed  with  filter 
paper  or  with  a  pipette,  and  a  cover-glass  put  on. 

Glycerin  mounts,  as  a  general  rule,  are  unsatisfactory.  Further- 
more, they  must  be  cemented  to  exclude  the  air.  This  can  be  done 
by  painting  a  ring  of  gold-size,  or  a  thick  solution  of  gum  shellac  in 
alcohol  to  which  a  little  castor  oil  has  been  added,  around  and  over 
the  edge  of  the  cover-glass.  Both  cover-glass  and  slide  must  be  cleaned 
free  from  glycerin  before  the  cement  is  applied.  A  camel's-hair  brush 
moistened  with  alcohol  is  the  best  means  of  removing  the  excess  of 
glycerin. 

Glycerin  jelly  is  a  more  satisfactory  mounting  medium  than  pure 
glycerin.  It  can  be  purchased  from  firms  dealing  in  microscopical 
supplies  and  needs  merely  the  application  of  heat  to  make  it  fluid. 
Specimens  can  then  be  mounted  in  it  in  the  usual  manner,  and  after 
being  allowed  to  cool,  do  not  require  cementing. 


GENERAL  TECHNIC.  21 

(2)  Balsam. — This  is  the  most  satisfactory  general  mounting 
medium.  It  has  an  advantage  over  glycerin  in  drying  down  perfectly 
hard  and  thus  needing  no  cement,  and  in  preserving  colors  more  per- 
manently. Its  disadvantage  is  that  its  refractive  index  is  so  high 
that  it  sometimes  obscures  the  finer  details  of  structure,  especially  of 
unstained  or  slightly  stained  specimens. 

Specially  prepared  Canada  balsam  is  dissolved  either  in  xylol  or' 
in  oil  of  cedar,  the  solution  being  made  of  any  desired  consistence. 
Xylol-balsam    dries  much  more  quickly  than    does    the    oil-of-cedar 
balsam. 

Preparatory  to  mounting  in  balsam,  stained  sections  must  be 
thoroughly  dehydrated  and  then  passed  through  some  medium  which 
is  miscible  with  both  alcohol  and  balsam.  This  medium,  which  at 
the  same  time  renders  the  section  transparent,  is  known  as  a  clearing 
medium.     For  celloidin  specimens  the  most  satisfactory  are: 

(i)   Oil  of  origanum  Cretici. 

(2)  Carbol-xylol  (xylol,  100  c.c,  carbolic-acid  crystals,  22  gm.), 
followed  by  pure  xylol. 

(3)  Xylol  and  cajeput  oil,  equal  parts,  followed  by  pure  xylol. 

After  clearing,  the  section  is  transferred  by  means  of  a  section- 
lifter  to  a  glass  mounting  slide.  In  case  oil  of  origanum  is  used,  it 
is  then  blotted  firmly  with  filter  paper  to  remove  the  excess  of  oil. 
Care  must  be  taken  to  have  the  filter  paper  several  layers  thick  in 
order  that  the  oil  may  be  completely  removed.  The  specimen  should 
also  be  blotted  firmly,  giving  the  oil  time  to  soak  into  the  paper.  These 
two  precautions  are  necessary  to  prevent  the  section  adhering  to  the 
paper  instead  of  to  the  slide.  After  blotting,  a  drop  of  balsam  is  placed 
upon  the  centre  of  the  specimen  and  a  cover-glass  put  on. 

When  xylol  is  used,  blotting  is  not  necessary.  Drain  off  the  excess 
of  oil,  put  a  drop  of  balsam  on  the  specimen  and  put  on  a  cover-glass. 

Paraffin  Sections. — The  technic  of  staining  and  mounting  paraffin 
sections  differs  from  that  of  celloidin  sections.  This  is  due  mainly 
to  the  fact  that  while  celloidin  is  transparent  and  may  remain  per- 
manently in  the  specimen,  paraffin  is  opaque  and  must  be  dissolved 
out  before  the  section  is  fit  for  microscopic  study. 

Bulk  staining  with  carmine  (page  19)  is  frequently  used  for  speci- 
mens which  are  to  be  embedded  in  paraffin.  Sections  may  be  counter- 
stained  if  desired. 

The  following  are  the  steps  to  be  followed  in  staining  and  mounting 
paraffin  sections: 


22  HISTOLOGICAL  TECHNIC. 

1.  To  attach  sections  to  slide: 

Place  a  drop  of  egg  albumen  (equal  parts  white  of  egg  and  glycerin 
to  which  a  little  carbolic  acid  may  be  added  for  preserving)  on  a 
slide,  and  spread  it  out  thin  with  the  finger. 

Place  a  few  drops  of  distilled  water  on  the  slide. 

Float  sections  on  the  water. 

Warm  gently  to  allow  sections  to  flatten — must  not  melt  paraffin. 

Pour  off  excess  of  water,  holding  the  ends  of  the  ribbons  to  prevent 
them  floating  off. 

Stand  slides  on  end  a  few  hours  to  allow  water  to  evaporate. 

2.  To  remove  parajfin: 

Place  slide  in  xylol  three  to  five  minutes. 

3.  To  stain  sections: 

Place  slide  in  fresh  xylol  three  minutes. 

Transfer  to  absolute  alcohol. 

Transfer  to  go-per-cent.  alcohol. 

Transfer  to  80-per-cent.  alcohol. 

Transfer  to  50-per-cent.  alcohol.     (May  be  omitted.) 

Transfer  to  water. 

Stain  with  an  aqueous  stain. 

Wash  in  water. 

Transfer  to  50-per-cent.  alcohol.     (May  be  omitted.) 

Transfer  to  80-per-cent.  alcohol. 

Transfer  to  90-per-cent.  alcohol. 

Transfer  to  absolute  alcohol. 

Transfer  to  xylol. 

Transfer  to  fresh  xylol. 

Mount  in  xylol-balsam. 

If  an  alcohol  stain  is  used  instead  of  an  aqueous  one,  the  carrying 
down  and  up  through  the  graded  alcohols  is  omitted. 

If  it  is  desired  to  stain  double  with  eosin-haematoxylin  (page  18)  use 
the  above  technic  in  staining  with  haematoxylin ;  then  the  alcoholic 
eosin  stain  before  final  transfer  to  absolute  alcohol. 

IX.   Injection. 

For  the  study  of  the  distribution  of  the  blood-vessels  in  tissues 
and  organs,  it  is  often  necessary  to  make  use  of  sections  in  which 
tlic  blood-vessels  have  been  injected  with  some  transparent  coloring 
matter.  The  injecting  fluid  most  commonly  used  is  a  solution  of 
colored  gelatin. 


GENERAL  TECHNIC.  23 

The  gelatin  solution  is  prepared  by  soaking  i  part  gelatin  in  from 
5  to  lo  parts  water — the  proportion  depending  upon  the  consistence 
desired — and  when  soft,  melting  on  a  water-bath. 

Various  dyes  are  used  for  coloring  the  gelatin,  the  most  common 
being  Prussian  blue  and  carmine. 

Prussian  blue  gelatin  is  prepared  by  adding  saturated  aqueous 
solution  Prussian  blue  to  the  gelatin  solution,  the  proportions  depend- 
ing upon  the  depth  of  color  desired.  Both  solutions  should  be  at  a 
temperature  of  60°  C.  After  thoroughly  mixing,  the  blue  gelatin  is 
filtered  through  cloth. 

Carmine  gelatin  is  prepared  by  first  dissolving  i  gm.  carmine 
in  30  c.c.  distilled  water.  To  this  is  added  ammonia  until  the  mix- 
ture becomes  a  dark  cherry  red.  A  lo-per-cent.  aqueous  solution  of 
acetic  acid  is  next  added,  drop  by  drop,  with  constant  stirring  until 
the  mixture  becomes  neutral.  The  carmine  and  gelatin  solutions 
both  being  at  about  60°  C,  are  now  mixed  in  the  desired  proportions. 
If  the  carmine  injection  mass  is  alkaline,  it  diffuses  through  the  walls 
of  the  vessels;  if  acid,  there  is  a  precipitation  of  the  carmine  which 
may  interfere  with  its  free  passage  through  the  capillaries.  If,  how- 
ever, the  alkaline  carmine  and  gelatin  be  first  mixed,  and  the  10- 
per-cent.  acetic  acid  solution  be  then  added  as  directed  above,  the 
precipitated  granules  are  so  fine,  even  with  an  acid  reaction,  that  they 
readily  pass  through  the  capillaries.  The  precipitation  of  the  car- 
mine in  the  shape  of  coarser  granules  is  of  advantage  when  it  is  desired 
to  have  an  injection  mass  which  will  fill  the  arteries  or  veins  only, 
without  passing  over  into  the  capillaries. 

The  in'ecting  apparatus  consists  of  a  vessel  which  contains  the 
injection  mass,  and  some  means  of  keeping  the  latter  under  a  con- 
stant but  easily  varied  pressure.  With  the  vessel  is  connected  a  tube 
ending  in  a  cannula,  through  which  the  injection  is  made. 

A  very  simple  apparatus  consists  of  a  shelf  which  can  be  raised 
and  lowered,  and  upon  which  the  vessel  stands.  The  tube  connect- 
ing with  the  cannula  may  be  attached  to  a  faucet  in  the  vessel  or  to 
a  bent  glass  tube  which  passes  into  the  top  of  the  vessel  and  acts  on 
the  principle  of  a  siphon. 

In  a  somewhat  more  elaborate  apparatus  the  injection  mass  is 
placed  in  a  closed  vessel,  and  this  is  connected  with  a  second  vessel 
containing  air  compressed  by  means  of  an  air  pump. 

Accurate  regulation  of  the  pressure  may  be  obtained  by  connect- 
ing the  injection  vessel  with  a  manometer. 


24  HISTOLOGICAL  TECHXIC. 

If  the  injection  is  to  occupy  considerable  time,  a  hot-water  bath 
in  which  the  gelatin  may  be  kept  at  an  even  temperature  is  also 
necessary. 

Whole  animals  or  separate  organs  may  be  injected.  For  inject- 
ing a  whole  animal,  the  animal,  which  is  usually  a  small  one  such  as 
a  guinea-pig,  rat,  mouse,  or  frog,  is  chloroformed,  the  tip  of  the  heart 
is  cut  away  and  a  cannula  is  inserted  through  the  heart  into  the  aorta. 
This  is  first  connected  with  a  tube  leading  to  a  bottle  containing 
warm  normal  saline  solution.  Pressure  is  obtained  in  the  same 
manner  as  above  described  for  the  injection  mass.  By  this  means 
the  entire  arterial  and  venous  systems  are  thoroughly  washed  out 
until  the  return  flow^  from  the  vena  cava  is  perfectly  clear.  The 
cannula  is  next  connected  with  the  tube  from  the  vessel  containing 
the  injection  mass,  the  pressure  being  only  sufficient  to  keep  the 
liquid  flowing.  When  the  injection  mass  flows  easily  and  freely 
from  the  ^■ena  cava,  the  vessel  is  tied  and  the  pressure  is  increased 
slightly  and  continued  until  the  color  of  the  injection  mass  shows 
clearly  in  the  superficial  capillaries.  The  aorta  is  now  tied  and  the 
animal  immersed  in  cold  water  to  solidify  the  gelatin.  After  the 
gelatin  becomes  hard,  the  desired  organs  are  removed  and  fixed  and 
hardened  in  the  usual  way.  Sections  of  injected  material  are  usually 
cut  rather  thick,  that  the  vessels  may  be  traced  the  greater  distance. 

Better  results  are  frequently  obtained  by  injecting  separate  organs. 
This  is  accomplished  by  injecting  through  the  main  artery  of  the 
organ  (e.g.,  the  lungs  through  the  pulmonary,  the  kidney  through  the 
renal).  The  injection  is  best  done  with  the  organ  in  situ,  although 
it  may  be  accomplished  after  the  organ  has  been  removed.  The 
method  is  the  same  as  given  above  for  injecting  an  animal  in  toto. 

The  so-called  double  injection  by  means  of  which  an  attempt  is 
made  to  fill  the  arteries  with  an  injection  mass  of  one  color  (red), 
while  the  veins  are  filled  with  an  injection  mass  of  another  color 
(blue),  often  gives  pretty,  but  usually  inaccurate  pictures,  it  being, 
as  a  rule,  impossible  to  confine  each  injection  mass  to  one  system. 
Double  injection  is  accomplished  by  first  washing  out  the  vessels 
with  normal  saline  and  then  connecting  the  artery  with  the  red  gela- 
tin, the  vein  with  the  blue  gelatin,  and  injecting  both  at  the  same 
time,  the  pressure  dri\ing  the  saline  out  of  the  vessels  into  the  tis- 
sues. The  difficulty  is  that  either  the  arterial  injection  carries  over 
into  the  veins,  or  the  venous  injection  carries  over  into  the  arteries. 
A  somewhat  more  accurate  method  is  first  to  inject  the  veins  with  an 


GENERAL  TECHXIC.  25 

injection  mass  in  which  the  coloring  matter  is  in  the  form  of  granules 
too  large  to  pass  through  the  capillaries,  and  then  to  inject  the  arte- 
ries and  capillaries  in  the  usual  manner.  This  method  is  especially 
useful  in  demonstrating  the  vessels  of  the  kidney,  liver,  and  gastro- 
intestinal canal. 


CHAPTER  II. 
SPECIAL  STAINING  METHODS. 

Of  these  only  the  more  common  will  be  described. 

(1)  SiLVER-KITRATE  METHOD  OF  StAINING  InTERCELLUI  AR  SUB- 
STANCE.— After  first  washing,  the  tissue,  e.g.,  omentum  or  cornea, 
is  placed  in  a  from  0.2-  to  i-per-cent.  solution  of  silver  nitrate,  or 
better,  protargol,  where  it  is  kept  in  the  dark  for  a  half-hour  or  more 
according  to  the  thickness  and  density  of  the  tissue.  The  specimen 
is  then  washed  in  water,  transferred  to  40-per-cent.  alcohol  and  placed 
in  the  direct  sunlight  until  it  assumes  a  light  brown  color.  It  is  then 
placed  in  fresh  80-per-cent.  alcohol  for  preservation. 

(2)  Chlorid  of  gold  in  i-per-cent.  aqueous  solution  is  used  in 
the  same  manner  for  demonstrating  connective-tissue  cells  and  their 
finer  processes. 

(3)  Weigert's  Elastic-tissue  Stain. — This  is  prepared  as 
follows: 

Fuchsin,  2  gm. 

Resorcin,  4  gm. 

Water,  200  c.c. 

These  are  boiled  for  five  minutes,  during  which  25  c.c.  of  liquor  ferri 
sesquichlorati  are  stirred  in.  The  result  is  a  precipitate  which  should 
be  filtered  out  after  the  liquid  has  become  cool.  After  drying,  200 
c.c.  of  95-per-cent.  alcohol  are  added  to  the  filtrate  and  boiled  until 
the  latter  dissolves.  Lastly,  4  c.c.  of  hydric  chlorid  are  added  to 
the  solution.  Sections  should  remain  in  the  stain  thirty  minutes, 
after  which  they  are  washed  in  alcohol  until  the  stain  ceases  to  be 
given  off. 

(4)  GoLGi's  Chrome-silver  Method  for  Demonstrating 
Secretory  Tubules. — Small  pieces  of  perfectly  fresh  tissue,  e.g., 
liver,  are  placed  in  the  following: 

Potassium  bichromate,  4-per-cent.  aqueous  solution,        4  vols. 
Osmic  acid,  i-per-cent.  aqueous  solution,  i   vol. 

After  three  days  they  are  transferred  without  washing  to  a  0.75-per- 
cent, aqueous  solution  of  silver  nitrate,  which  should  be  changed  as 

26 


SPECIAL  STAINING  METHODS.  27 

soon  as  a  precipitate  forms.  The  specimens  remain  in  the  second 
silver  solution  from  two  to  three  days,  after  which  they  are  rapidly  de- 
hydrated, embedded  in  celloidin,  and  cut  into  rather  thick  sections. 

(5)  Mallory's  Phosphomolybdic  Acid  H.ematoxylin  Stain  for 
Connective  Tissue. — Thin  sections  are  placed  for  from  two  to  ten 
minutes  in  a  lo-per-cent.  aqueous  solution  of  phosphomolybdic  acid. 
They  are  then  washed  in  distilled  water  and  tranferred  to: 

Phosphomolybdic  acid,  ic-per-cent.  aqueous  solution,       100. o  c.c. 
Distilled  water,  200.0  c.c. 

Haematoxylin  crystals,  i .  75  gm. 

Carbolic-acid  crystals,  5- 00  gm. 

The  phosphomolybdic  acid  and  water  are  first  mixed,  after  which 
the  haematoxylin  and  carbolic  acid  are  added. 

After  staining  from  ten  to  twenty  minutes  the  sections  are  washed 
in  distilled  water,  placed  for  five  minutes  in  50-per-cent.  alcohol,  then 
in  strong  alcohol,  cleared  in  xylol  and  mounted  in  xylol-balsam.  This 
stain  works  best  after  Zenker's  fluid  fixation. 

(6)  Mallory's  Phosphotungstic  Acid  H^ematoxyiin  Stain  for 
Connective  Tissue. 

Haematoxylin  (or  htematein  ammonium),  0,1  gm. 

Water,  80.      c.c. 

Phosphotungstic   acid   (Merck),    lo-per-cent.   aqueous 

solution,  20.      c.c. 

The  haematoxylin  should  be  dissolved  in  a  little  water  with  the 
aid  of  heat  and,  when  cool,  added  to  the  rest  of  the  solution. 
Allow  to  ripen  for  several  weeks  or  months.  Or,  if  it  is  desired 
to  use  immediately,  the  solution  can  be  ripened  by  the  addition 
of  10  c.c.  of  a  1/4-per-cent.  solution  of  potassium  permanganate. 

Tissues  should  be  fixed  in  Zenker's  fluid  (p.  8). 

1.  Treat  sections  with  iodin  solution  to  remove  mercury  precipi- 
tate, 5  to  10  minutes  (p.  9.) 

2.  Several  changes  95-per-cent.  alcohol. 

3.  Water. 

4.  One-fourth-per-cent.  aqueous  solution  potassium  permanganate, 
5  to  10  minutes. 

5.  Wash  in  water. 

6.  Five-per-cent.  aqueous  solution  oxalic  acid,  5  to  10  minutes. 

7.  Wash  thoroughly  in  water. 

8.  Phosphotungstic  acid  haematoxylin  solution,  twelve  to  twenty- 
four  hours. 


28  HISTOLOGICAL  TECHNIC. 

9.  Dip  for  a  few  seconds  in  95-per-cent.  alcohol. 

10.  Clear  in  carbol-xylol  and  xylol  and  mount  in  xylol-damar. 

(j)  Mallory's  Aniline  Blue  Stain  for  Connective  Tissue. — 
Tissues  should  be  fixed  in  Zenker's  fluid  (p.  8.) 

1.  Stain  thin  sections  in  a  o.  2-per-cent.  aqueous  solution  of  acid 
fuchsin  for  five  to  ten  minutes.     (This  step  may  be  omitted.) 

2.  Stain  in  the  following  solution  for  twenty  minutes: 

Aniline  blue  (soluble  in  water),  0.5  gm. 

Orange  G.,  2  .0  gm. 

Phosphomolybdic  acid,  i-per-cent.  aqueous  solution,    100. o  cc. 

3.  Decolorize  in  several  changes  of  95-per-cent.  alcohol. 

4.  Clear  in  carbol-xylol  and  xylol  and  mount  in  xylol-damar. 

(8)  OsMic-ACiD  Stain  for  Fat. — For  this  purpose  osmic  acid 
is  used  in  a  i-per-cent.  aqueous  solution.  The  method  is  especially 
useful  for  demonstrating  developing  fat,  fatty  secretions  (mammary 
gland),  and  fat  absorption  (small  intestine).  Very  small  bits  of  the 
tissue  are  placed  in  the  osmic-acid  solution  for  from  twelve  to  twenty- 
four  hours.  They  are  then  hardened  in  graded  alcohols,  embedded 
in  celloidin,  and  the  sections  mounted  in  glycerin. 

(9)  Jenner's  Blood  Stain. 

Water-soluble    eosin    (Griibler),    i-per-cent.    aqueous 

solution,  100  cc. 

Methylene  blue — pure  (Griibler),  i-per-cent.  aqueous 

solution,  100  cc. 

Mix,  and  after  standing  24  hours,  filter.     The  filtrate  is  dried 

at  65°  C,  washed,  again  dried  and  powdered. 

To  make  the  staining  solution,  0.5  gm.  of  the  powder  is  dissolved 
in  TOO  cc.  pure  methyl  alcohol.  Blood  smears  stain  in  from  two  to 
five  minutes.  They  are  then  washed  in  water,  dried,  and  mounted  in 
balsam. 

This  solution  acts  as  a  fixative  as  well  as  a  stain. 


CHAPTER  III. 
SPECIAL  NEUROLOGICAL  STAINING  METHODS. 

Weigert's  Method  of  Staining  Medullated  Nerve  Fibres. 

In  preparing  material  for  the  Weigert  method,  two  points  are  to 
be  kept  in  mind:  ist,  proper  fixation  and  preservation  of  the  myeHn 
sheaths;  2d,  treatment  (mordanting)  with  a  reagent  which  enters 
into  combination  with  the  myelin,  the  result  being  that  the  myelin 
sheaths  stain  specifically  with  haematoxylin.  Formalin  fulfils  the 
first  requirement,  the  bichromates  the  first  and  second.  Consequently 
the  material  may  be  fixed  and  hardened  in  bichromate,  and,  if  not  to  be 
used  immediately,  is  best  kept  in  formalin  to  avoid  overhardening. 
Or  the  material  may  be  fixed  and  kept  in  formalin  and  impregnated 
with  the  bichromate  before  using,  the  latter  being  done  before  dehy- 
drating in  alcohol.  Further  mordanting,  which  is  usually  done,  espe- 
cially when  the  material  has  been  kept  for  some  time  in  formalin 
or  alcohol,  is  for  the  purpose  of  intensifying  the  stain. 

Material  is  fixed  in  one  of  the  following  fluids: 

(a)  Muller's  fluid  (page  6). 

(b)  Potassium  bichromate,  5-per-cent.  aqueous  solution. 

(c)  Formalin,  lo-per-cent.  aqueous  solution. 

(d)  Formalin,  i  volume;  potassium  bichromate,  5-per-cent.  aque- 
ous solution,  9  volumes. 

In  Muller's  fluid  or  in  plain  potassium-bichromate  solution  a 
hardening  of  two  days  to  four  weeks  is  required ;  in  formalin  or  formalin- 
bichromate  from  a  week  to  ten  days  is  sufficient.  All  material  is  better 
kept  until  used  in  5-per-cent.  to  lo-per-cent.  formalin  solution  than  in 
alcohol.  The  specimens  are  then  hardened  in  graded  alcohols,  em- 
bedded in  celloidin,  and  sections  cut  in  the  usual  way.  Material  fixed 
in  formalin  should  be  placed  for  several  days  in  the  following: 

Chrome  alum,  ''  i  gm. 

Potassium  bichromate,  3  gm. 

Water,  100  c.c. 

before  hardening  in  alcohol. 

Sections  from  material  fixed  in  any  of  the  chrome-salt  solutions 
are  placed  for  from  twch'e  to  twenty-four  liours  in  a  saturated  aqueous 

29 


30  HISTOLOGICAL  TECHNIC. 

solution  of  neutral  cupric  acetate  diluted  with  an  equal  volume  of 
water.  The  cupric  acetate  forms  some  combination  with  the  tissues 
which  intensifies  their  staining  qualities,  thus  acting  like  the  chrome 
salts  as  a  mordant. 

iVfter  mordanting,  the  sections  are  washed  in  water  and  trans- 
ferred to  the  following  staining  fluid: 

Haematoxylin  crystals,  i  gm. 

Alcohol,  95-per-cent.,  10  c.c. 

Lithium  carbonate — saturated  aqueous  solution,  i   c.c. 

Water,  90  c.c. 

This  solution  must  either  be  freshly  made  before  using,  the  haema- 
toxylin being  dissolved  first  in  the  alcohol,  or  the  hasmatoxylin  may 
be  kept  in  lo-per-cent.  alcoholic  solution,  the  lithium  carbonate  in 
saturated  aqueous  solution,  and  the  staining  fluid  made  from  these 
as  needed. 

Sections  remain  in  the  haematoxylin  solution  from  two  to  twenty- 
four  hours,  the  longer  time  being  required  for  staining  the  finer  fibres 
of  the  cerebral  and  cerebellar  cortices.  They  are  then  washed  in  water 
and  decolorized  in  the  following: 

Potassium  ferricyanid,  2  . 5  gm. 

Sodium  biborate,  2.0  gm. 

Water,  300.0  c.c. 

While  in  the  decolorizer,  sections  should  be  gently  shaken  or  moved 
about  with  a  glass  rod  to  insure  equal  decolorization.  In  the  decolor- 
izer the  sections  lose  the  uniform  black  which  they  had  on  removal 
from  the  haematoxylin.  They  remain  in  the  decolorizing  fluid  until 
the  gray  matter  becomes  a  light  gray  or  yellow  color,  in  sharp  con- 
trast with  the  white  matter  which  remains  dark.  Sections  are  then 
washed  in  several  waters  to  remove  all  traces  of  decolorizer,  and  de- 
hydrated in  alcohol. 

Weigert-Pal  Method. — In  this  modification  of  the  Weigert 
method,  material  hardened  in  formalin  should  be  further  hardened  in 
potassium  bichromate  5-per-cent.  for  two  weeks,  or  in  copper  bichro- 
mate 3-per-cent.  for  about  a  week,  after  which  it  may  be  cut  and 
stained  without  further  mordanting.  Sections  from  material  hard- 
ened in  the  other  above-mentioned  ways  are  mordanted  in  a  3-  to  5- 
per-cent.  aqueous  solution  of  potassium  bichromate  instead  of  in  the 
copper-acetate  solution.  After  rinsing  in  water  the  sections  are 
stained   in   haematoxylin   as   in   the  ordinary  Weigert  method.     The 


SPECIAL  NEUROLOGICAL  STAINING  METHODS.  31 

lithium  carbonate  may,  however,  be  omitted.  They  are  then  washed 
and  transferred  to  a  0.25-per-cent.  solution  of  potassium  permanganate, 
where  they  remain  from  one-half  to  two  minutes,  after  which  they 
are  again  washed  and  placed  in  the  following: 

Oxalic  acid,  i  gm. 

Potassium  sulphite,  i  gm. 

Water,  200  c.c. 

In  this  solution  differentiation  takes  place,  the  medullary  sheaths 
remaining  dark,  while  the  color  is  entirely  removed  from  the  rest  of 
the  tissue.  If  the  section  is  still  too  dark,  it  may  again  be  carried 
through  the  permanganate  and  oxalic-acid  solutions,  rinsing  in  water 
between  changes,  until  sufficiently  decolorized. 

All  formalin-fixed  material  is  best  stained  by  the  Weigert-Pal 
method.  An  intensification  of  the  stain,  especially  of  the  A'ery  fine 
fibres,  may  sometimes  be  obtained  by  placing  the  sections  for  a  minute 
in  a  o.  5-per-cent.  aqueous  solution  of  osmic  acid  before  decolorizing. 

Marchi's  Method  for  Staining  Degenerating  Nerves. 

Small  pieces  of  tissue  are  fixed  and  hardened  for  from  seven  to  ten 
days  in  Mtiller's  fluid.  Thin  slices  of  the  tissue  are  then  transferred 
to  a  solution  of  one  part  i-per-cent.  osmic  acid  and  two  parts  Miiller's 
fluid,  in  which  they  remain  from  two  to  seven  days.  After  embedding 
and  sectioning  in  the  usual  manner,  sections  are  mounted,  usually 
without  further  staining,  in  xylol-balsam.  The  treatment  with  Miiller's 
fluid  so  affects  the  normal  medullary  sheaths  that  they  will  not  take 
the  osmic-acid  stain,  but  appear  yellowish-brown,  while  the  degenerating 
sheaths  (probably  fatty)  stain  black.  The  result  is  a  positive  picture 
of  stained  degenerating  fibres  in  contrast  with  the  stained  normal  and 
unstained  degenerated  fibres  as  seen  after  Weigert  staining.  Another 
advantage  of  the  Marchi  method  is  that,  as  the  picture  is  a  positive  one, 
an  early  or  slight  degeneration  may  be  recognized  which  would  escape 
notice  in  material  stained  by  Weigert's  method;  on  the  other  hand, 
in  a  long-standing  degeneration  when  the  medullary  sheaths  ha\'e 
completely  disappeared  and  their  places  have  been  taken  by  connective 
tissue,  there  being  no  degenerated  myelin  remaining,  the  Marchi 
method  is  inapplicable. 

Busch's  modification  of  the  Marchi  method  gives  sharp  pictures 
and  has  the  advantag;e  of  allowing;  formaldehvd  fixation  and  harden- 


32  HISTOLOGICAL  TECHNIC. 

ing.  Tissues  thus  treated  are  placed  for  from  five  to  seven  days  in  a 
solution  of  one  part  osmic  acid,  three  parts  iodate  of  sodium,  and  300 
parts  water.     They  are  then  embedded,  cut,  and  mounted  as  usual. 

GoLGi  Methods  of  Staining  Nerve  Tissue. 

The  Golgi  methods  in  most  common  use  at  present  are  the  fol- 
lowing: 

(i)  GoLGi  Silver  Methods. — (a)  Slow  Method. — Blocks  of  tis- 
sue are  placed  for  several  months  in  a  3-per-cent.  aqueous  solution 
of  potassium  bichromate.  Small  pieces  of  the  tissue  are  then  trans- 
ferred immediately  to  a  o.  75-per-cent.  aqueous  solution  of  silver 
nitrate.  This  is  changed  several  times  or  until  no  more  precipitate 
is  formed.  In  the  last  silver  solution  they  remain  for  from  one  to 
three  days.  The  only  method  of  determining  whether  the  tissue  has 
been  sufficiently  long  in  the  bichromate  is  to  try  at  intervals  small 
bits  of  the  tissue  in  the  silver  solution  until  a  satisfactory  result  is 
secured.  Sections  should  usually  be  from  50  to  8o/<  thick  and  are 
mounted  in  balsam  without  a  cover-glass. 

(b)  Rapid  Method. — Small  pieces  of  tissue,  2  to  4  mm.  thick, 
are  placed  in  the  following  solution  for  from  two  to  six  days,  the  time 
depending  upon  the  age  and  character  of  the  tissue,  the  temperature 
at  which  fixation  is  carried  on,  and  the  elements  which  it  is  desired 
to  impregnate: 

Osmic  acid,  i-per-cent.  aqueous  solution,  i   part. 

Potassium  bichromate,  3. 5-per-cent.  aqueous  solution,  4  parts. 

As  a  rule,  the  longer  the  hardening  the  fewer  are  the  elements  stained, 
but  these  few  are  clearer.  The  tissue  is  next  transferred  to  silver 
nitrate  as  in  the  slow  method.  Pieces  of  tissue  should  be  tried  each 
day  until  a  satisfactory  result  is  obtained.  The  pieces  may  be  kept 
in  silver  nitrate  some  time,  but  not  in  alcohol,  and  are  better  cut  with- 
out embedding,  the  pieces  being  simply  washed  in  95-per-cent.  alcohol 
several  hours,  then  gummed  to  the  block  with  celloidin,  cut  in  95- 
pcr-cent.  alcohol,  and  mounted  as  in  the  slow  method. 

(c)  Mixed  Method. — Specimens  are  placed  in  the  bichromate 
solution  for  about  four  days,  then  from  one  to  three  days  in  the  osmium- 
bichromate  mixture  (see  Rapid  Method),  after  which  they  are  trans- 
ferred to  the  silver  solution  (see  Slow  Method). 


SPECIAL  NEUROLOGICAL  STAIXIXG  METHODS.  33 

(d)  Formalin-bichromate  Method. — Tissues  are  placed  for  from 
two  to  six  days  in  the  following  solution: 

Formalin,  lo  to  20  parts. 

Potassium     bicliromate,     3-per-cent.     aqueous 

solution,  90  to  80  parts. 

Subsequent  treatment  with  silver  is  the  same  as  in  the  previously 
described  method.  The  results  resemble  those  of  the  slow  method. 
The  specimens  may  be  kept  in  strong  alcohol.  The  method  is  satis- 
factory only  for  the  adult  cerebrum  and  cerebellum. 

(2)  GoLGi  BiCHLORiD  METHOD. — Material,  which  need  not  be  cut 
into  small  pieces,  remains  for  several  months  in  the  potassium- 
bichromate  solution  (see  Slow  Silver  Method),  after  which  it  is  trans- 
ferred to  a  0.25-per-cent.  to  i-per-cent.  aqueous  solution  of  mercuric 
chlorid  for  from  four  to  twelve  months  or  longer,  the  solution  being 
changed  as  often  as  discolored.  The  degree  of  impregnation  must  be 
determined  by  frequently  testing  the  material,  but  is  usually  indicated 
by  the  appearance  of  small  white  spots  on  the  surface  of  the  tissue. 

A  modification  of  the  bichlorid  method,  known  as  the  Cox-Golgi 
Method,  often  gives  good  results.  The  following  fixing  solution  is 
used : 

Potassium  bichromate,  5-per-cent.  aqueous  solution,     20  parts. 
Mercuric  chlorid,  5-per-cent.  aqueous  solution,  20  parts. 

Distilled  water,  40  parts. 

After  mixing  the  above,  add 

Potassium  chromate,  5-per-cent.  aqueous  solution,         16   parts. 

Tissues  remain  in  this  iiuid  for  from  two  to  five  months. 

In  the  Golgi  silver  methods  the  result  of  the  treatment,  first  with 
bichromate  and  then  with  silver  nitrate,  is  that  a  precipitate  is  formed 
in  the  tissue,  a  chromate  or  some  other  silver  salt,  which  in  favorable 
cases  is  largely  confined  to  certain  of  the  nerve  cells  and  their  processes. 
It  must  l)e  remembered  that  only  a  few  of  the  cells  and  processes  are 
stained,  these  often  only  partially,  and  that  other  irregular  precipita- 
tions arc  usually  present.  In  the  mercury  methods,  the  bichromate  of 
potassium  and  the  bichlorid  of  mercury  may  be  used  coml)incd  in  the 
same  solution.  There  are  other  modifications  of  the  Golgi  methods,  in 
which  similar  precipitates  of  other  metallic  salts  are  secured. 

Golgi  specimens  should  be  dehydrated  and  embedded  as  rapidly 
as  possible.  This  is  especially  true  of  specimens  treated  by  the  rapid 
and  the  mixed  methods.     Those  treated  bv  tlie  slow  sih'er  method 


34  HISTOLOGICAL  TECHNIC. 

and  by  the  bichlorid  method  are  more  permanent,  and  more  time  may 
be  taken  with  their  dehydration.  Sections  should  be  cut  thick  (75  to 
loo/i)  and  mounted  in  xylol-balsam.  After  the  rapid  method,  it  is 
safer  to  mount  without  a  cover- glass;  after  the  slow  method,  specimens 
may  be  mounted  with  or  without  a  cover.  The  balsam  should  be  hard, 
and  melted  at  the  time  of  using.     (See  Mounting,  page  21.) 

Cajal's  Methods  for  Staining  the  Neurofibrils  in  the 

Nerve-cells. 

In  these  methods,  besides  the  neurofibrils,  the  cell  processes  and 
especially  the  axis  cylinders  are  often  beautifully  displayed,  the  stain 
giving  a  picture  in  this  respect  much  more  general  than  that  of  the 
Golgi  methods,  but  much  more  specific,  and  sharper  than  that  of  the 
ordinary  stains. 

The  methods  consist  mainly  of  two  steps:  (i)  The  staining  of 
the  tissue  in  a  solution  of  silver  nitrate;  (2)  the  further  reduction  of 
the  silver  stain  with  a  weak  photographic  developer.  Three  methods, 
or  variations,  are  here  given: 

(i)  Pieces  about  0.5  cm.  thick  are  placed  in  a  liberal  quantity  of 
from  i-per-cent.  or  i .  5-per-cent.  (new-born  or  embryonic  mammalian 
material)  to  5-per-cent.  (adult  material)  solution  of  silver  nitrate  and 
kept  at  a  temperature  of  32°  to  40°  C.  for  two  to  five  days.  When 
properly  stained  (shown  by  a  yellowish  or  light  brown  coloration  of 
freshly  cut  surfaces)  the  pieces  are  very  briefly  rinsed  in  distilled  water 
and  placed  in:  pyrogallol  (or  hydroquinone)  i  gram,  distilled  water 
100  c.c,  formalin  5  to  10  c.c,  for  twenty-four  hours  or  more.  They 
are  then  washed  a  few  minutes  in  water  and  transferred  to  95-per-cent. 
alcohol,  which  is  changed  when  discolored,  and  where  they  may  often 
be  kept  for  some  time  without  injury.  They  may  then  be  embedded 
in  celloidin  or  parafhn  and  sections  cut,  usually  15-25//  in  thickness. 
Different  depths  of  the  blocks  of  tissue  usually  vary  in  stain,  the  most 
favorable  being  intermediate  between  the  surface  and  centre  of  the 
block.  Celloidin  sections  usually  keep  well  in  95-per-cent.  alcohol. 
They  may  be  cleared  in  carbol-xylol,  rinsed  in  xylol,  and  mounted  in 
xylol-balsam  or  xylol-damar  in  the  usual  way.  In  delicate  objects 
(study  of  pathological  changes  in  neurofibrils)  it  may  be  best  to  abbre- 
viate the  dehydration,  and  block  and  cut  without  infiltration  with 
celloidin. 

(2)  Pieces  are  first  placed  in  95-per-cent.  alcohol  or  in  absolute 
alcohol  (32°  to  40°  C.)  for  twenty-four  hours.     For  neurofibrils  it  is 


SPECIAL  NEUROLOGICAL  STAINING  METHODS.  35 

better  to  add  from  0.25  c.c.  to  i  c.c.  of  ammonium  hydrate  to  each 
10  c.c.  of  the  alcohoh  They  are  then  treated  with  silver  nitrate  i-per- 
cent.  or  1.5-per-cent.,  as  in  (i).  This  method  gives  better  pictures 
of  the  cell  processes  and  axis  cylinders  and  a  better  fixation  of  the  cells. 

(3)  Pieces  are  first  placed  in  distilled  water  100  c.c,  formalin 
20  c.c,  ammonia  i  c.c,  for  twenty-four  hours  at  32°-4o°  C,  washed 
in  water  twelve  to  twenty-four  hours,  and  then  treated  with  silver 
nitrate  i-per-cent.  or  1.5-per-cent.,  as  in  (i).  This  method  gives 
pictures  of  the  terminations  of  nerve  fibres  on  the  periphery  of  nerve- 
cells  and  their  dendrites  (end-feet  or  end-buttons  of  Auerbach). 

In  general  it  is  best  to  a^'oid,  in  the  above  methods,  any  excessive 
exposure  to  the  light  while  the  pieces  are  in  the  silver  bath  (especially 
when  the  pieces  are  very  small),  though  they  may  be  brought  into 
the  light  for  examination  and  while  being  transferred  to  the  reducing 
fluid. 

Nissl's  Method. 

This  method  is  useful  for  studying  the  internal  structure  of  the 
nerve  cell.  It  depends  upon  a  rapid  fixation  of  the  tissue,  its  subse- 
quent staining  with  an  aniline  dye,  and  final  decolorization  in  alcohol. 

The  aniline  dye  most  commonly  used  is  methylene  blue.  There 
are  many  variations  and  modifications  of  Nissl's  method.  The  fol- 
lowing is  simple  and  gives  uniformly  good  results: 

Specimens  are  first  fixed  in  mercuric-chlorid  solution  (page  7), 
in  formalin  (lo-per-cent.  aqueous  solution),  or  in  absolute  alcohol, 
and  embedded  in  celloidin. 

Thin  sections  are  stained  in  a  i-per-cent.  aqueous  solution  of 
pure  methylene  blue  (Griibler).  The  sections  are  gently  warmed  in 
the  solution  until  steam  begins  to  be  gi^'en  oft".  They  are  then  washed 
in  water  and  differentiated  in  strong  alcohol.  The  degree  of  decolor- 
ization which  gives  the  best  results  can  be  learned  only  by  practice. 
Several  alcohols  must  be  used,  and  the  last  alcohol  must  be  perfectly 
free  from  methylene  blue.  The  sections  are  cleared  in  equal  parts 
xylol  and  cajeput  oil  and  mounted  in  xylol-balsam.  A  contrast  stain 
may  be  obtained  by  having  a  little  eosin  or  erythrosin  in  the  last  alcohol. 

General  References  for  Further  Study  of  Technic. 

Freeborn:  Histological  Technic.  Reference  Handbook  of  ^ledical  Sciences, 
vol.  iv. 

Lee:  The  ^Microtomist's  \'ade-mecum. 
Mallorv  and  Writrhl:  Patholosjical  Technic. 


PART  II. 
THE   CELL. 


CHAPTER  I. 
THE  CELL. 

In  the  simplest  forms  of  animal  life  the  entire  body  consists  of  a 
little  albuminous  structure,  the  essential  peculiarity  of  which  is  that 
it  possesses  properties  which  we  recognize  as  characteristic  of  living 
organisms.  This  albuminous  material  basis  of  life  is  known  as  pro- 
toplasm, while  the  structure  itself  is  known  as  a  cell.  Within  the 
cell  is  usually  found  a  specially  formed  part,  the  nucleus.  Peripher- 
ally some  cells  are  limited  by  a  distinct  cell  wall  or  cell  membrane. 


2 

3 

4- 
5 

6 
7 


Fig.  I. — Diagram  of  a  typical  cell,  i,  Cell  membrane.  2,  Metaplasm  granules. 
3,  Karyosome  or  net-knob.  4,  Hyaloplasm.  5,  Spongioplasm.  6,  Linin  network. 
7,  Nucleoplasm.  8,  Attraction-sphere.  9,  Centrosome.  10,  Plastids.  11,  Chro- 
matin network.     12,  Nuclear  membrane.     13,  Nucleolus.     14,  Vacuole. 

An  actively  multiplying  cell  contains  a  minute  structure  associated 
with  the  reproductive  function  and  known  as  the  centrosome. 

A  typical  cell  thus  consists  of  the  following  structures  (Fig.  i): 
(i)  The  cell  body;  (2)  the  cell  membrane;  (3)  the  nucleus;  (4)  the 
centrosome.  Of  these  the  cell  body  is  the  only  one  present  in  all 
cells.  Most  animal  cells  have  no  cell  membrane.  A  few  cells  con- 
tain, in  their  fully  developed  condition,  no  nuclei.  In  many  mature 
cells  it  is  impossible  to  distinguish  a  centrosome. 

All  plants  and  animals  consist  of  cells  and  their  derivatives,  and 
if  an  attempt  be  made  to  resolve  any  of  the  more  complex  li\ing  struc- 
tures into  its  component  elements,  it  is  found  that  the  smallest  possible 

39 


40 


THE  CELL. 


subdivision  still  compatible  with  life  is  the  cell.     The  cell  may  there- 
fore be  considered  as  the  histological  element  or  unit  of  structure. 

I.  The  Cell  Body. — This  consists  of  a  viscid  semi-fluid  substance, 
belonging  to  the  general  class  of  albumens.  It  is  of  complex  chemical 
composition  containing  the  elements  carbon,  hydrogen,  oxygen  and 
nitrogen  in  quite  constant  proportions,  and  smaller  variable  quanti- 
ties of  phosphorus,  sulphur,  iron  and  other  substances.  It  contains 
a  peculiar  nitrogenous  proteid,  plastin.  Structurally  it  can  be  differ- 
entiated into  a  formed  element,  spongioplasm,  and  a  homogeneous 
Q  element,     hyaloplasm.       Dis- 

tributed along  the  spongio- 
plastic  network  are  minute 
granules,  microsomes.  The 
exact  relations  which  these 
elements  bear  to  one  another 
and  to  the  cell  as  a  whole 
have  been  the  subject  of  much 
investigation  and  speculation. 
The  earlier  cytologists  con- 
cerned themselves  with  the 
question  as  to  whether  proto- 
plasm was  homogeneous  {i.e., 
a  mere  solution  or  at  most  a 
mixture  of  various  substances) 
or  had  a  definite  structure. 
The  theory  of  a  structureless 
protoplasm  having  been  long 


Fig.  2. — Diagram  Illustrating  Theories  of 
Protoplasmic  Structure,  a,  Fibrillar  theory';  b, 
granule  theon,-;  c,  "foam"  theory.  (The  gen- 
eral structure  of  cell  body  and  nucleus  cor- 
responds.) 


since  abandoned,  the  question  as  to  the  character  of  the  protoplasmic 
structure  still  remains  unanswered. 


Altmann'.s  granule  theory  considers  protoplasm  as  composed  of  fine  granules 
embedded  in  a  gelatinous  intergranular  substance.  Altmann  believed  these 
granules  the  ultimate  vital  elements,  and  for  this  reason  gave  them  the  name  of 
bioblasts  (Fig.  2,  b). 

According  to  Butschli,  |jrotoplasm  is  a  foam  or  emulsion,  the  microscopic  ap- 
jjearancc  of  which  can  be  simulated  by  artificial  emulsions.  He  ascribes  the 
appearance  of  a  reticulum  to  the  fact  that  each  little  foam  space  forms  a  complete 
cavity  filled  with  fluid,  the  cut  walls  of  these  spaces  giving  a  reticular  appearance  on 
section  (Fig.  2,  c  and  Fig.  3). 

Other  investigators  consider  protoplasm  as  made  up  of  (i)  a  fibrillar  element, 
either  in  the  form  of  a  network  of  anastomosing  fibrils  (cytoreticulum)  or  of  a  felt- 
work  of  independent  fibrils  (fiilar  mass  or  miton),  and  (2)  a  fluid  or  semi-fluid  sub- 


THE  CELL. 


41 


stance  which  fills  in  the  meshes  of  the  reticulum  or  separates  the  fibrils  (interfilar 
mass  or  paramiton)  (Fig.  2,  a). 

That  the  question  as  to  the  ultimate  structure  of  protoplasm  still  remains 
unanswered  is  dependent  mainly  upon  the 
extreme  technical  difficulties  which  have  con- 
fronted the  cytologist.  Living  protoplasm  has 
a  homogeneous  glossy  appearance,  showing 
even  under  the  highest  magnification  rarely 
more  than  a  granular  structure.  It  is  usually 
only  after  death  of  the  cell  and  the  use  of 
chemical  fixatives  and  stains,  that  the  so-called 
"structure"  of  protoplasm  becomes  visible. 
How  closely  the  picture  presented  by  such 
chemically  treated  protoplasm  corresponds  to 
the  structure  of  -living  protoplasm  is  as  yet 
undetermined.  It  is  quite  possible  that  the 
structure  of  protoplasm  is  not  entirely  uniform. 
It  certainly  differs  somewhat  both  as  to  struc- 
ture and  chemical  composition  in  dift"erent 
cells.  It  also  differs  in  the  same  cell  under 
different  functional  conditions.  These  varia- 
tions may  account,  in  part  at  least,  for  the 
lack  of  uniformity  of  results  of  different 
observers. 

Protoplasm  is  thus  probably  best  con- 
sidered as  the  material  basis  of  cell 
activity,  i.e.,  of  life,  rather  than  as  a 
substance  having  fixed  and  definite  chem- 
ical or  morphological  characteristics. 

It  is  convenient  to  use  the  term  pro- 
toplasm to  mean  the  entire  substance  of 
the  cell,  karyoplasm  to  designate  the 
protoplasm  of  the  nucleus,  and  cytoplasm 
the  protoplasm  of  the  cell  body  exclusive 
of  the  nucleus. 

Peculiar  bodies  known  as  plastids 
(Fig.  i)  are  of  frequent  occurrence  in 
vegetable  cells,  and  are  also  found  in 
some  animal  cells.  They  are  apparently 
to  be  regarded  as  a  dift'erentiation  of  the 
cytoplasm,    but    possess    a    remarkable 

degree  of  independence,   being  capable  of  subdivision  and  in  some 
cases  of  existence  outside  of  the  cell. 


Fi 


-Foam  or  emulsion  structure 
of  protoplasm  according  to 
Biitschli  (Biitschli).  A,  Epi- 
dermal cell  of  the  earthworm. 
B,  Peripheral  cytoplasm  of  sea 
urchin's  egg.  C,  Artificial  emul- 
sion of  olive  oil,  sodium  chloride 
and  water. 


42  THE  CELL. 

In  addition  to  the  granules  which  are  apparently  an  integral  part 
of  the  protoplasmic  structure,  other  granules  and  various  cell  "inclu- 
sions" occur,  to  which  the  term  metaplasm  {paraplasm,  deutoplasm) 
granules,  has  been  applied  (Fig.  i).  Some  of  these  are  intimately 
associated  with  the  cell  activities  and  represent  either  food  substances 
in  process  of  being  built  up  into  the  protoplasm  of  the  cell  or  waste 
products  of  cell  metabolism.  Others,  such  e.g.,  as  the  glycogen  granules 
of  the  liver  cell  or  the  mucous  granules  of  the  mucous  cell,  are  specific 
secretion  products.  Still  others  are  fat  droplets,  pigment  granules,  and 
various  excrementitious  substances. 

When  the  protoplasm  of  a  cell  can  be  differentiated  into  a  cen- 
tral granular  area  and  a  peripheral  clear  area,  the  former  is  known  as 

endo plasm,  the  latter  as  exo plasm.  When 
the  exoplasm  forms  a  distinct  limiting  layer, 
but  blends  imperceptibly  with  the  rest  of 
the  protoplasm,  it  is  known  as  the  crusta. 

In  some  cells  minute  channels  or  canals 
are  present  in  the  cytoplasm  (Fig.  4), 
These  channels  may  contain  branching  proc- 
esses from  other  cells,  forming  what  is 
known  as  a  trophospongium,.  Some  in- 
FiG.     4  —Intracellular    canals    tracellular  canals  are  apparently  secretory 

(trophospongium)  of    a   gan-     .  .  . 

glion  cell  (E.  Holmgren).  m  character  and  may  communicate  with 

fine  intracellular  secretory  channels.  In 
this  way  the  secretion  of  such  cells  as  the  serous  cells  forming  the 
demilunes  of  mucous  tubules  (p.  195),  or  of  the  parietal  cells  of  the 
stomach  glands  (Fig.  136),  is  carried  to  the  lumen. 

2.  The  Cell  Membrane  (Fig.  i). — This  is  present  in  but  few  ani- 
mal cells,  and  is  a  modification  of  the  peripheral  part  of  the  protoplasm. 
In  most  vegetable  cells  the  membrane  is  the  most  conspicuous  part  of 
the  cell  and  was  responsible  for  the  name  "cell"  which  the  seven- 
teenth-century botanists,  overlooking  the  importance  of  the  enclosed 
protoplasm,  gave  to  the  little  spaces  or  cavities  of  which  they  thought 
plants  composed.  When  a  membrane  surrounds  the  cell,  it  is  known 
as  the  pellicula;  when  cells  lie  upon  the  surface,  and  only  the 
free  surface  of  the  cells  is  covered  by  a  membrane,  it  is  known  as 
the  cuticula. 

3.  The  Nucleus  (Fig.  i). — This  is  a  vesicular  body  embedded  in 
the  cytoplasm.  The  typical  nucleus,  like  the  typical  cell,  is  spheroidal, 
but  the  shape  of  the  nucleus  varies  for  different  cells  and  corresponds 


THE  CELL.  43 

somewhat  to  the  shape  of  the  cell  body,  e.g.,  the  rod-shaped  nucleus  of 
the  elongated  smooth  muscle  cell.  It  may  also  be  modified  by  intra- 
cellular pressure  as,  e.g.,  in  the  mucous  cell  and  in  the  fat  cell. 

The  position  of  the  nucleus  is  usually  near  the  center  of  the  cell. 
It  may,  however,  be  eccentric.  Such  eccentricity  may  be  due  to 
pressure  of  cell  contents  as,  e.g.,  in  the  mucous  cell  and  in  the  fat  cell. 
Considered  by  earlier  cytogists  an  unessential  part  of  the  cell,  the 
nucleus  is  now  known  to  be  most  intimately  associated  with  cellular 
activities.  It  is  not  only  essential  to  the  carrying  on  of  the  ordinary 
metabolic  processes  of  the  cell,  but  is  an  active  agent  in  the  phenomena 
of  mitosis,  which  in  most  cases  determine  cell  reproduction. 

As  a  rule,  each  cell  contains  a  single  nucleus.  Some  cells  contain 
two  nuclei  (quite  common  in  the  liver  cell,  rare  in  the  ovum  and  in 
the  nerve  cell).  A  few  cells  contain  many  nuclei,  e.g.,  the  multinuclear 
"giant"  cells  of  the  spleen,  bone-marrow,  and  certain  tumors.  Some 
cells,  such  as  the  human  red  blood  cell  and  the  respiratory  epithelium, 
are,  in  their  mature  condition,  non-nucleated.  All  non-nucleated 
cells,  however,  contained  nuclei  in  the  earher  stages  of  their  develop- 
ment. Non-nucleated  cells,  while  capable  of  performing  certain 
functions,  are  wholly  incapable  of  proliferation.  The  non-nucleated 
condition  must,  therefore,  be  regarded  as  not  only  a  condition  of  matur- 
ity, but  of  actual  senility,  at  least  so  far  as  reproductive  powers  are 
concerned. 

In  some  of  the  lowest  forms  of  animal  life,  the  nuclear  material 
instead  of  being  grouped  to  form  a  definite  body  or  nucleus,  is  more 
or  less  evenly  distributed  as  granules  through  the  cytoplasm. 

Chemically  the  nucleus  is  extremely  complex,  being  composed  of 
the  proteids  nuclein,  paranuclein,  linin,  paralinin,  and  amphipyrenin. 

Morphologically  also  the  nucleus  is  complex,  much  of  the  apparent 
structural  differentiation  being  determined  by  the  staining  reactions  of 
the  different  elements  when  treated  with  certain  aniline  dyes.  The 
nuclear  structures  and  their  relations  to  the  chemical  constituents  of 
the  nucleus  are  as  follows: 

(a)  The  nuclear  membrane  {amphipyrenin).  This  forms  a  limit- 
ing membrane  separating  the  nucleus  from  the  cell  protoplasm.  It 
is  doubtful  whether  the  nuclear  membrane  is  different  either  chemic- 
ally or  morphologically  from  the  nucleoreticulum.  It  is  wanting  in 
some  nuclei.  When  present  it  appears  from  its  staining  reactions  to 
be  structurally  continuous  with,  and  chemically  identical  with,  in  some 
cases,  the  linin,  in  others,  the  chromatin  of  the  intranuclear  network. 


44  THE  CELL. 

It  may  be  complete,  or  fenestrated  allowing  free  communication  between 
the  cytoplasm  and  the  nuclear  contents. 

(b)  The  intranuclear  network,  or  nuclear eticulum,  consists  of  a 
chromatic  element  (nuclein  or  chromatin)  and  of  an  achromatic  ele- 
ment {linin).  The  linin  constitutes  the  groundwork  of  the  reticulum 
along  which  the  chromatin  granules  are  distributed.  At  nodal  points 
of  the  network  there  are  often  considerable  accumulations  of  chro- 
matin. These  nodal  points,  at  first  thought  to  be  nucleoli,  are  now 
known  as  false  nucleoli^  or  karyosomes.  Instead  of  a  distinct  network 
there  may  be  disconnected  threads  or  simply  granules  of  chromatin. 
Chromatin  is  the  most  characteristic  of  the  chemical  constituents 
of  the  nucleus,  the  only  one  which  contains  phosphoric  acid,  and  also, 
apparently,  the  only  nuclear  substance  which  is  always  transmitted 
from  parent  to  daughter  cell  in  cell-division.  Fine  granules  have  been 
described  as  occurring  in  the  linin,  differentiated  from  chromatin  by 
the  fact  that  they  are  most  susceptible  to  acid  dyes,  while  chromatin 
takes  basic  dyes. 

(c)  The  micleolus  or  plasmosome  (paranuclein,  pyrenin)  is  a  small 
spherical  body  within  the  nucleus.  Not  infrequently  there  are  several 
nucleoli.  Similar  cells  vary  as  to  the  number  of  nucleoli  they  contain. 
The  same  cell  may  vary  as  to  the  number  of  its  nucleoli  under  varying 
functional  conditions.  The  nucleolus  stains  intensely  with  basic  dyes. 
Its  function  is  unknown. 

id)  Karyoplasm  {nucleoplasm,  nuclear  fluid,  nuclear  sap).  This 
is  the  fluid  or  semi-fluid  material  which  fills  in  the  meshes  of  the  nucleo- 
reticulum. 

While  the  nucleus  is  a  perfectly  distinct  structure  capable  in  some 
animal  and  in  some  vegetable  cells  of  moving  about  more  or  less 
actively  in  the  cytoplasm,  and  is  usually  separated  by  a  membrane 
from  the  rest  of  the  cell,  a  marked  simflarity  exists  between  the  structure 
of  nucleoplasm  and  cytoplasm.  This  similarity  is  emphasized  by  the 
absence  in  some  resting  cefls  of  any  nuclear  membrane,  by  the  apparent 
direct  continuity  in  some  cases  of  nucleoreticulum  and  cytoreticulum, 
and  by  the  continuity  of  karyoplasm  and  cytoplasm  in  all  cells  during 
ceIl-di\'ision. 

4.  The  centrosoine  (Fig.  5)  is  a  small  spheroidal  body  found  some- 
times in  the  nucleus,  or  more  commonly  in  the  cytoplasm  near  the  nu- 
cleus. In  actively  dividing  cells  the  centrosomc  is  frequently  double, 
this  being  apparently  in  preparation  for  the  succeeding  cell-division. 
In  some  cases  the  centrosome  is  triple  or  even  multiple.      It  was  first 


THE  CELL.  4o 

found  in  the  ovum  and  described  as  peculiar  to  that  cell.  It  is  now  be- 
lieved to  occur  in  most,  if  not  in  all,  animal  cells.  It  usually  consists  of 
(i)  a  minute  central  granule  or  granules — the  cenlriole,  which  stains 
intensely  with  iron-hasmatoxylin,  and  outside 
of  which  is  (2)  a  clear  zone,  the  attraction 
sphere.  From  this  centre,  radiations  extend 
outward  into  the  cytoplasm.  There  is  much 
confusion  of  terms  in  connection  with  the  cen- 
trosome,  the  term  centrosome  being  by  some 
applied  to  the  entire  structure  including  the 
radiating  fibrils,  by  others  to  the  central  granule 
only,  by  still  others  to  the  central  granule  plus  ^ 

,  .        Fig.    5.  —  Spermatogonium 

the  surrounding  clear  area.  By  some  the  radia-  from  frog  (Hermann), 
tions  are  beheved  to  be  composed  of  a  different  ^^^^^  ora^uTaTtio^n 
substance   than   the  general  cytoplasm,  which      sphere  or  aster.    Nucleus 

.  .         ■       T  contains  a  plasmosome. 

is   designated  archoplasm.      Ihe  main  signm- 

cance  of  the  centrosome  is  in  connection  with  cell-division,  under  which 

head  it  will  be  further  considered  (page  48). 

Vital  Properties  of  Cells. 

It  has  already  been  noted  that  the  essential  peculiarity  of  the  cell 
is  that  it  possesses  certain  properties  which  are  characteristic  of  life. 
By  this  is  meant  that  a  cell  is  able:  i.  To  nourish  itself  and  to  grow — 
metabolism.  2.  To  do  work — function.  3.  To  respond  to  stimula- 
tion— irritability.  4.  To  move — motion.  5.  To  produce  other  cells 
— reproduction. 

In  the  simplest  forms  of  animal  life,  where  a  single  cell  constitutes 
the  entire  individual,  all  of  these  functions  are  performed  by  the  one 
cell.  In  all  higher,  that  is,  multicellular  animals,  there  are  not  only 
many  cells  but  many  kinds  of  cells,  and  this  morphological  differen- 
tiation corresponds  to  a  physiological  differentiation,  each  group  of 
cells  developing  along  certain  well-defined  lines  for  the  performance 
of  its  own  special  function. 

I.  Metabolism. — This  term  is  used  to  designate  those  cellular 
acti\"ities  which  have  to  do  with  the  nutrition  of  the  cell.  A  cell  is 
able  (i)  to  take  up  from  without  substances  suitable  for  its  nutrition 
and  to  transform  these  into  its  own  peculiar  structure,  and  (2)  to  dis- 
pose of  the  waste  products  of  intracellular  acti\ities.  The  former  is 
known  as  constructive  metabolism  or  aimhoIis)n.  the  latter  as  destruc- 
tive nuiabolism  or  kalabolism. 


46  THE  CELL. 

2.  Function. — This  is  the  special  work  which  it  is  the  part  of 
the  cell  to  perform.  It  varies  greatly  for  different  cells.  Some  cells, 
as,  e.g.,  the  surface  cells  of  the  skin,  appear  to  act  mainly  as  protec- 
tion for  more  delicate  underlying  structures.  Other  cells — gland 
cells — in  addition  to  maintaining  their  own  nutrition,  produce  specific 
substances  (secretions),  which  are  of  great  importance  to  the  body  as 
a  whole.  Still  other  cells,  e.g.,  nerve  cells  and  muscle  cells,  have  the 
power  to  store  up  their  food  substances  in  such  a  way  as  to  make 
them  available  in  the  form  of  energy.  This  appears  to  be  accom- 
plished by  the  building  up  within  the  cell  of  highly  complex  and,  con- 
sequently, unstable  molecular  combinations.  By  reduction  of  these  un- 
stable combinations,  molecules  of  greater  stability  and  less  complexity 
are  formed.  This  results  in  the  .transformation  of  potential  into  kinetic 
energy,  and  the  expenditure  of  this  energy  is  expressed  in  function. 

3.  Irritability  is  that  property  which  enables  a  cell  to  respond  to 
external  stimuli.     Cells  vary  in  respect  to  their  irritability,  the  most 


-A^ 


m^^ 


''"^^^i-.  :■^5^-^^'■^''■  .  .-,  ",'-iJ'''"~;>,  -^^^|!^'.-. 


Fig.  6. — Amoeboid  Movement.     Successive  changes  in  shape  and  position  of  fresh- 
water amoeba. 

markedly  irritable  cells  in  higher  animals  being  those  of  the  neuro- 
muscular mechanism.  Stimulation  may  be  mechanical,  electrical, 
thermal,  chemical,  etc.  The  response  of  the  cell  to  certain  forms  of 
chemical  stimulation  is  known  as  chemotaxis.  Some  substances 
attract  cells  (positive  chemotaxis) ;  others  repel  cells  (negative  chemo- 
taxis). Stimuli  other  than  chemical  possess  similar  properties,  as 
indicated  by  the  terms  thermotaxis,  galvanotaxis,  etc.  Some  cells 
are  so  specialized  as  to  react  only  to  certain  kinds  of  stimulation,  e.g., 
the  retinal  cells  only  to  light  stimuli. 

4.  Motion. — This  is  dependent  wholly  upon  the  protoplasm  of  the 
cell,  and  is  exhibited  in  several  somewhat  different  forms. 

(a)  Amoeboid  Movement.  This  consists  in  the  pushing  outward 
by  the  cell  of  processes  (pseudopodia).  These  may  be  retracted  or 
may  draw  the  cell  after  them.  In  this  way  the  cell  may  change  both 
its  shape  and  position  (Fig.  6). 


THE  CELL. 


47 


(b)  Protoplasmic  Movement.  This  occurs  wholly  within  the  limits 
of  the  cell,  changing  neither  its  shape  nor  position.  It  occurs  in  both 
plant  and  animal  cells,  and  consists  of  a  sort  of  circulation  or  "stream- 
ing" of  the  protoplasm.  It  is  evidenced  by  the  movement  of  minute 
granules  present  in  the  protoplasm,  by  changes  in  the  position  of  the 
nucleus,  etc. 

(c)  Ciliary  Movement.  This  is  the  whipping  motion  possessed 
by  little  hair-like  processes  called  cilia,  which  project  from  the  surfaces 
of  some  cells. 

Certain  cells  which  are  specialized  for  the  particular  purpose  of 
motion  as,  e.g.,  muscle  cells,  possess  such  powers  of  contraction  that 
they  are  able  to  move  not  only  themselves  but  other  parts  with  which 
they  are  connected.  This  power  of  contractility  is  dependent  upon 
the  spongioplasm,  the  hyaloplasm  playing  a  more  passive  role.  In 
muscle  cells  the  highly  developed  contractile  powers  appear  to  be  due 
to  the  excessive  development  and  peculiar  arrangement  of  the  spongio- 
plasm. 

5.  Reproduction.— The  overthrow  of  the  long-held  biological  fal- 
lacy of  spontaneous  generation  was  soon  followed  by  the  downfall  of 
a  similar  theory  regarding  the 
origin  of  cells.  We  now  know- 
that  all  cells  are  derived  from 
cells,  and  that  the  vast  num- 
ber and  complex  of  cells  which 
together  form  the  adult  human 
body  are  all  derived  from  a 
single  primitive  cell,  the  ovum. 

Reproduction  of  cells  takes 

place  in  two  ways,  by  direct 

cell  division  or  amitosis,  and 

by    indirect    cell    division     or 

mitosis.      In  both  amitosis  and     Fig.  7.— Epithelial  Cells  from  Ovary  of  Cockroach, 
rr,,-f^o,V  fU     J-    •   •  r  .1  1.     Showing  Nuclei  Dividing  Amiloticallv.  (Wheeler.) 

mitosis  the  division  of  the  cell 

body  is  preceded  by  division  of  the  nucleus. 

Direct  Cell-division— Amitosis  (Figs.  7  and  8).— In  this  form  of 
cell-division  the  nucleus  di\idcs  into  two  daughter  nuclei  without  any 
apparent  preliminary  changes  in  its  structure.  The  division  of  the 
nucleus  may  or  may  not  be  followed  by  di\-ision  of  the  cell  body,  in  the 
latter  case  resulting  in  the  formation  of  polynuclear  cells.  This  form  of 
cell-diA-ision  is  uncommon  in  higher  animals  where  Flemming  consid- 


48 


THE  CELL. 


ers  it  a  degenerative  phenomenon  rather  than  a  normal  method  of  cell- 
increase.     It  is  a  common  method  of  cell-division  in  the  protozoa. 

Indirect  Cell-division — Mitosis  (Figs.  9,  10). — In  this  form  of 
cell-division  also,  the  nucleus  divides  into  two  daughter  nuclei,  and  the 
cell  into  two  daughter  cells,  but  only  after  they  have  passed  through 
certain  characteristic  and  complicated  changes.     These  changes  occur 

as  a  continuous  process, 
but  it  is  convenient  for 
clearness  of  description  to 
arbitrarily  divide  them  into 
stages  or  phases.  Thus  we 
recognize  in  mitosis :  (a)  the 
prophase;  (b)  the  metaphase; 
(c)  the  anaphase;  (d)  the 
telophase.  The  prophase  is 
the  stage  of  preparation  on 
the  part  of  the  nucleus  for 
division;  the  metaphase, 
the  actual  separation  of  the 
nuclear  elements;  the  ana- 
phase, the  formation  of  the 
two  daughter  nuclei;  the 
telophase,  the  reconstruc- 
///,  fibrils  tion  of  the  two  daughter 
resting  nuclei  and  the  divi- 
sion of  the  cytoplasm. 

(a)  The  Prophase  (Fig.  9,  B,  C,  D)  is  marked  by  the  following 
changes: 

I.  The  centrosome,  if  single,  divides  into  two  daughter  centrosomes. 
In  most  actively  dividing  cells,  however,  the  centrosome  is  at  this 
stage  already  double  (Fig.  9,  A)  having  divided  as  early,  frequently,  as 
the  anaphase  of  the  preceding  mitosis. 

The  two  daughter  centrosomes,  each  surrounded  by  its  attraction 
sphere,  now  move  apart  but  remain  connected  by  fibrils,  probably 
deri\-ed  from  the  linin  (Fig.  9,  B).  These  fibrils  form  the  central  or 
achromatic  spindle.  Two  other  sets  of  fibrils  radiate  from  each  centro- 
some— one,  known  as  the  polar  rays,  passes  out  toward  the  periphery  of 
the  cell;  the  other,  known  as  the  mantle  fibres,  extends  from  the  centro- 
some to  the  chromosomes  (Fig.  9,  C).  The  two  centrosomes  with  their 
fibres  constitute  the  amphiaster. 


M 

Fig.  8. — Epithelial  cell  from  bladder  showing  ami- 
totic  division    of    its   nucleus.       (Nemileff.)       / 
Cytoplasm;     //,  two  daughter  nuclei 
uniting  daughter  nuclei. 


THE  CELL. 


4U 


2.  During  or  immediately  following  the  formation  of  the  amphiaster, 
important  changes  take  place  in  the  nucleus.  It  increases  in  size  and 
loses  the  reticular  appearance  of  the  resting  nucleus,  its  chromatic  ele- 
ments becoming  arranged  in  a  long  spireme-thread  or  in  several  shorter 
threads,  the  closed  skein  or  closed  spireme.  This  next  becomes  thicker 
and  more  loosely  arranged,  thus  forming  the  open  spireme.     That  some 


Fig.  9. — Diagrams  of  Successive  Phases  of  Mitosis. 

A,  Resting  cell,  with  reticular  nucleus  and  true  nucleolus;  c,  attraction  sphere  with  two 
centrosomes. 

B,  Early  prophase.  Chromatin  forming  continuous  thread — the  spireme;  nucleolus 
still  present ;'a,  amphiaster;  the  two  centrosomes  connected  by  fibrils  of  achromatic  spindle. 

C,  Later  prophase.  Segmentation  of  spireme  to  form  the  chromosomes;  achromatic 
spindle  connecting  centrosomes;  polar  rays;  mantle  fibres;  fading  of  nuclear  membrane. 

D,  End  of  prophase.  Monaster — mitotic  figure  complete;  ep,  chromosomes  arranged 
around  equator  of  nucleus;  fibrils  of  achromatic  spindle  connecting  centrosomes;  mantle 
fibres  passing  from  centrosomes  to  chromosomes.  (E.  B.  Wilson,  "The  Cell,"  The  ]Mac- 
niillan  Co  ) 

chemical  as  well  as  morphological  change  has  taken  place  in  the  trans- 
formation of  the  reticulum  of  the  resting  nucleus  into  the  spireme  is 
shown  by  the  marked  increase  in  staining  intensity,  the  spireme  taking  a 
much  darker  stain  than  the  reticulum.  Late  in  the  prophase  the 
nucleolus  and  nuclear  membrane  disappear.  The  cytoplasm  and 
karyoplasm  then  become  continuous  and  both  spireme  and  amphiaster 
lie  free  in  the  general  cell  protoplasm  (Fig.  9,  C). 
4 


50 


THE  CELL. 


3.  The  spireme  next  breaks  up  into  a  number  of  segments — chro- 
viosomes  (Fig.  9,  C).  These  are  usually  rod-shaped  at  first,  later  they 
may  become  U's  or  V's  or  may  even  become  spheroidal.  The 
chromosomes  now  arrange  themselves  regularly  around  the  equator  of 
the  nucleus,  their  closed  ends  being  directed  centrally. 

The  details  of  the  transformation  of  the  reticulum  into  chromosomes 
vary.     In  some  cases  a  single  spireme-thread   is  formed.     In  others 


Fig.   10. — Diagrams  of  Successive  Phases  of  Mitosis. 

E,  Metaphase.  Longitudinal  cleavage;  splitting  of  chromosomes  to  form  daughter 
chromosomes,  ep;  n,  cast-off  nucleolus. 

F,  Anaphase.  Daughter  chromosomes  passing  along  fibrils  of  achromatic  spindle 
toward  centrosomes;  division  of  centrosomes;  if,  interzonal  fibres  or  central  spindle. 

G,  Late  anaphase.     Formation  of  diaster;  beginning  division  of  cell  body. 

H,  Telophase.  Reappearance  of  nuclear  membrane  and  nucleolus;  two  complete 
daughter  cells,  each  containing  a  resting  nucleus.  (E.  B.  Wilson,  "The  Cell,"  The  Mac- 
millan  Co.) 

the  spireme-thread  first  splits  longitudinally  into  two  threads  before 
segmenting  into  chromosomes.  Again  the  spireme-thread  may  show 
segmentation  into  chromosomes  from  the  beginning.  In  still  other 
cases  the  chromosomes  apparently  form  directly  from  the  reticulum 
without  the  intervention  of  the  spireme  stage.  It  is  most  important  to 
note  that  while  the  number  of  chromosomes  varies  for  different  species 
of  plants  and  animals,  it  is  fixed  and  characteristic  for  a  given  species. 


THE  CELL.  51 

Thus  in  Ascaris  megalocephala  (much  used  for  study  on  account  of 
its  small  number  of  chromosomes)  the  number  is  4,  in  the  mouse  24, 
in  man,  estimated  by  some  as  16,  by  others  24.  This  means  that  when- 
ever mitosis  occurs  in  Ascaris,  the  spireme-thread  invariably  segments 
into  4  chromosomes.  Chromosomes  and  amphiaster  now  constitute 
the  mitotic  figure  which  at  this  stage  is  known  as  the  monaster,  its  for- 
mation marking  the  end  of  the  prophase. 

(b)  Metaphase  (Fig.  10,  E).  This  marks  the  beginning  of  actual 
division  of  the  nucleus.  Each  chromosome  splits  longitudinally 
(longitudinal  cleavage)  into  two  daughter  chromosomes,  each  containing 
exactly  one-half  the  chromatin  of  the  parent  chromosome.  U-  and  \- 
shaped  chromosomes  always  begin  to  split  at  the  apex,  from  which 
point  the  separation  extends  to  the  open  ends. 

(c)  Anaphase  (Fig.  10,  F,G). — An  equal  number  of  daughter  chromo- 
somes now  travels  along  the  fibrils  of  the  achromatic  spindle — appar- 
ently under  the  influence  of  the  mantle  fibres — toward  each  daughter 
centrosome  around  which  they  become  grouped.  In  this  way  are 
formed  two  daughter  stars,  the  mitotic  figure  being  known  at  this  stage 
as  the  diaster  (Fig.  10,  G).  These  daughter  stars  are  at  first  connected 
by  the  fibrils  of  the  achromatic  spindle.  In  this  stage  may  also  occur 
beginning  division  of  the  cell  body.  In  actively  dividing  cells  each 
centrosome  frequently  undergoes  division  at  this  stage,  resulting  in 
four  centrosomes  to  the  cell. 

(d)  Telophase  (Fig.  10,  H). — This  is  marked  by  division  of  the  cell 
protoplasm  and  consists  of  a  cycle  of  changes,  by  means  of  which  each 
group  of  daughter  chromosomes  is  transformed  into  the  chromatin 
network  of  a  resting  nucleus.  These  changes  are  the  same  as  those 
described  in  the  prophase,  but  occur  in  the  reverse  order,  the  chromo- 
somes uniting  to  form  the  spireme,  and  the  spireme  becoming  trans- 
formed into  the  nuclear  network.  The  result  is  the  formation  of 
two  daughter  cells.  The  nuclear  membrane  reappears,  as  does  also 
the  nucleolus.  Each  daughter  cell  is  thus  provided  with  a  resting 
nucleus.  The  fact  that  the  number  of  chromosomes  which  enter  into 
the  formation  of  the  chromatic  reticulum  of  the  nucleus  of  each 
daughter  cell  is  the  same  as  the  number  into  which  the  spireme  of 
the  parent  cell  divided,  has  suggested  the  hypothesis  that  the  chro- 
mosomes maintain  their  identity  even  during  the  resting  stage. 

The  time  required  for  the  mitotic  process  is  usually  from  one-half 
to  three-quarters  of  an  hour.  Exceptionally  it  is  prolonged  to  several 
hours. 


52  THE  CELL. 

The  parts  which  the  several  cell  structures  play  in  mitosis  have  been 
the  subjects  of  much  study  and  are  as  yet  not  fully  determined. 

As  to  the  behavior  of  the  chromatic  portion  of  the  mitotic  figure 
little  doubt  exists.  It  originates  in  the  chromatic  portion  of  the  nuclear 
reticulum  of  the  parent  cell  and  its  destination  is  the  chromatic  portion 
of  the  reticulum  of  the  daughter  cells. 

The  role  of  the  centrosome  in  mitosis  is  not  so  clear.  It  has  been 
called  the  "dynamic  centre"  of  the  cell  because  in  most  cases  it  appears 
to  be  the  active  agent  in  initiating  and  probably  further  directing  the 
mitotic  process.  The  origin  of  the  astral  fibres  is  not  always  the  same. 
In  Infusoria  the  centrosome  is  found  within  the  nucleus  and  both 
amphiaster  and  chromosomes  are  of  nuclear  origin.  In  some  of  the 
higher  plants  the  amphiaster  is  derived  wholly  from  the  spongioplasm.  In 
the  egg  cells  of  Echinoderm,  part  of  the  amphiaster  (central  spindle) 
is  of  nuclear,  the  remainder  (asters)  of  cytoplasmic  origin.  That  the 
centrosome  is  not  always  the  active  factor  in  mitosis  is  shown  by  the 
fact  that  in  the  higher  plants  no  centrosome  can  be  demonstrated 
during  any  stage  of  mitosis,  and  also  that  in  some  cases  the  chromo- 
somes divide  without  previous  division  of  the  centrosome.  Between 
mitotic  periods  the  centrosome  with  or  without  its  aster  may  remain 
as  an  integral  part  of  the  resting  cell.  It  may,  on  the  other  hand, 
entirely  disappear  during  the  resting  stage. 

It  is  through  the  above-described  process  of  cell-division  that  new 
cells  are  produced  to  replace  those  worn  out  as  a  result  of  their  labors 
or  destroyed  by  injury.  It  is  through  the  same  process  that  the  vast 
number  of  cells  which  make  up  the  adult  body  are  developed  from 
one  original  cell — the  ovum.  Such  powers  of  evolution  are  not,  how- 
ever, inherent  in  the  ovum  itself,  but,  in  sexual  reproduction,  are  ac- 
quired only  after  its  union  with  germinal  elements  from  the  male.  This 
union  of  male  and  female  germinal  elements  is  known  as  fertilization 
of  the  ovum. 

Fertilization  of  the  Ovum. 

Prior  to  and  in  preparation  for  fertilization,  both  male  and  female 
cells  must  pass  through  certain  changes.  These  are  known  as  matu- 
ration of  the  spermatozoon  on  the  male  side  (p.  315)  and  of  the  ovum  on 
the  female  (p.  328). 

The  spermatozoon  (Fig.  11)  is  developed  from  a  cell  of  the  seminifer- 
ous tubule  of  the  testis.  The  nucleus  of  this  cell  so  divides  its  chro- 
mosomes that  each  spermatozoon  contains  just  one-half  the  number  of 


THE  CELL. 


chromosomes  characteristic  of  cells  of  the  species.  These  are  contained 
in  the  head  of  the  spermatozoon,  which  thus  represents  the  nucleus 
of  the  male  sexual  cell,  the  middle  piece  probably  containing  the  centro- 
some,  the  tail  piece  the  remains  of  the  protoplasm. 

The  nucleus  of  the  ovum  or  germinal  vesicle  also  passes  through 
a  series  of  changes  by  which  it  loses  one-half  its  chromosomes.  The 
germinal  vesicle  or  nucleus  of  the  ovum  first  under- 
goes mitotic  division  with  the  usual  longitudinal 
cleavage  of  its  chromosomes  and  the  formation  of 
two  daughter  nuclei.  One  of  these  and  its  centrosome 
are  extruded  from  the  cell  as  the  first  polar  body. 
The  remaining  nucleus  and  centrosome  again  divide 
mitotically,  only  in  this  second  division,  instead  of 
the  usual  longitudinal  cleavage  of  chromosomes,  by 
which  each  daughter  nucleus  is  provided  with  the 
same  number  of  chromosomes  as  the  mother  nucleus, 
the  chromosomes  simply  separate,  one-half  going  to 
each  daughter  nucleus.  One  of  the  daughter  nuclei 
and  its  centrosome  are  now  extruded  as  the  second 
polar  body.  The  polar  bodies  ultimately  disappear, 
as  does  also  the  centrosome  remaining  within  the  egg. 
This  leaves  in  the  now  matured  ovum  a  single  nucleus, 
which  is  known  as  the  female  pronucleus,  and  which 
contains  one-half  the  number  of  chromosomes  charac- 
teristic of  cells  of  the  species. 

During  this  process  in  some  animals — in  others 
after  its  completion — the  spermatozoon  enters  the 
ovum.  The  head  of  the  spermatozoon  becomes  the 
male  pronucleus,  the  middle  piece  becomes  a  centrosome,  while 
the  tail  is,  in  some  instances  at  least,  left  behind  as  the  spermato- 
zoon enters  the  egg.  The  chromatin  of  the  male  next  becomes  ar- 
ranged as  chromosomes.  Male  and  female  pronuclei  now  lose  their 
limiting  membranes  and  approach  each  other,  their  chromosomes 
intermingling.  ^4^  each  pronucleus  contained  one-half  the  number,  the 
monaster  thus  formed  contains  the  full  number  of  cliromosomcs  charac- 
teristic of  tJie  species.  Meanwhile  the  male  centrosome,  formed  from 
the  body  of  the  spermatozoon,  divides  into  two  daughter  centrosomes. 
These  with  their  radiating  fibrils  have  the  same  arrangement  relative 
lo  the  monaster  of  mingled  male  and  female  chromosomes,  alrcadv 
described  under  mitosis.     Bv  lonijitudinal  clca\-a<re  of  these  chromo- 


FiG.  I  I. — Human 
Spermatozoa.  (Af- 
ter Retzius.)  I, 
Head  seen  on  flat; 
2,  head  seen  on 
edge;  k,  head;  ;», 
body;/,  tail;  e,  end 
piece. 


54 


THE  CELL. 


somes,  as  in  ordinary  mitosis,  two  sets  of  daughter  chromosomes  are 
formed.  Each  set  passes  along  the  filaments  of  the  achromatic  spindle 
to  its  centrosome.  Thus  is  formed  the  diaster.  By  continuation  of 
the  mitotic  process  two  new  nuclei  are  formed,  each  nucleus  contain- 


membrane  of 
ovum 


nucleus  of 
ovum 
entering  sper- 
matozoon 
protoplasm  of 
ovum  with 
deutoplasm 
granules 


^  —  female  pronucleus 


male  pronucleus 


■\   _  chromosome  of  female 
-■'''  pronucleus 


,  chromosome  of  male 
pronucleus 


centrosome 


^  female     pronu- 
cleus 


head    of    sper- 
— matozoon  with 
centrosome 


centrosome 


male  pronu- 
cleus 


female  pro- 
nucleus 


chromosome 
from  female 
pronucleus 


.,  -__    chromosome 
' .  /  from  male 

7  pronucleus 


Fig.  12. — Diagram  of  Fertilization  of  the  Ovum.  (The  somatic  number  of  chromosomes 
being  four.)  (From  Bohm  and  von  Davidoff,  after  Boveri.) 
I,  Ovum  surrounded  by  spermatozoa,  only  one  of  which  is  in  the  act  of  penetration. 
Toward  the  latter  the  protoplasm  of  the  ovum  sends  out  a  process;  2,  Head  of  spermato- 
zoon has  entered  ovum,  its  body  becoming  the  male  centrosome,  its  tail  having  disap- 
peared; 3,  The  head  of  spermatozoon  has  become  the  male  pronucleus.  Male  and  female 
pronuclei  approach  each  other.  Between  them  is  the  (male)  centrosome;  4,  The  spiremes 
of  male  and  female  pronuclei  have  each  formed  two  chromosomes.  The  centrosome  has 
divided;  5,  Male  and  female  chromosomes  have  mingled  and  by  longitudinal  cleavage  (see 
Mitosis,  p.  51)  have  become  eight.  These  become  arranged  in  the  equatorial  plane  of 
the  ovum.  Mantle  fibres  extend  from  centrosomes  to  chromosomes;  6,  Division  of  the 
ovum;  two  daughter  cells,  each  containing  a  daughter  nucleus.  Each  daughter  nucleus 
contains  four  chromosomes,  two  derived  from  each  pnmucleus. 


THE  CELL. 


ing  the  number  of  chromosomes  characteristic  of  the  species,  and  each 
being  made  up  equally  of  male  and  female  chromosome  elements.  Thus 
occurs  the  first  division  of  the  fertihzed  ovum  into  tw^o  daughter  cells. 


SEGMENTA- 
TION   CAVITY. 


Fig.   13. — Segmentation  of  the  Ovum.     (P>om  Gerrish,  after  van  Beneden.) 
a,  Two-cell  stage  resulting  from  first  division  of  fertilized  ovum;  ^,  four-cell  statue; 
c,  d,  e,  later  stages.    A,  Differentiation  into  inner  and  outer  cells;  5,  Formation  of  segmenTa- 
tion  cavity;  C",  Embryonic  vesicle,  showing  two  primary  germ  lavers.  Outer  cells,  ectoderm; 
inner  cells,  entoderm. 


56 


THE  CELL. 


By  similar  mitotic  processes  ttiese  two  cells  become  four,  the  four  cells 
become  eight,  etc.     This  is  known  as  segmentation  of  the  ovum. 

The  earlier  generations  of  these  cells  are  morphologically  alike  and 
are  known  as  hlastomeres.  Soon,  however,  these  cells  become  spread 
out  and  at  the  same  time  differentiated  into  two  primary  germ  layers. 
The  outer  of  these  is  known  as  the  ectoderm  or  epiblast,  the  inner  as 
the  entoderm  or  hypoblast.  Between  these  two  layers  and  derived 
from  them  a  third  layer  is  formed,  the  mesoderm  or  mesohlast.  These 
three  la  vers  constitute  the  blastoderm. 


e^6c„  s 


Fig.  14. — The  Two  Primary  Germ  Layers;  from  transverse  section  through  primitive 
groove  of  a  chick  of  27  hours'  incubation,  a,  Ectoderm  (outer  germ  layer) ;  b,  entoderm 
(inner  germ  layer) ;  c,  mesoderm  (middle  germ  layer) ;  d,  anlage  of  notochord. 

As  to  what  determines  and  controls  fertilization,  comparatively 
little  is  known.  As  in  ordinary  mitosis,  the  origin  of  the  centrosome 
is  obscure.  In  some  forms,  at  least,  the  centrosome  of  the  spermatid 
enters  into  the  formation  of  the  middle  piece  of  the  spermatozoon. 
The  male  centrosome  thus  enters  the  ovum.  It  is  also  known  that  in 
some  eggs  the  egg-centrosome  disappears  soon  after  the  extrusion 
of  the  second  polar  body,  and  that  the  centrosome  of  the  fertilized 
egg  develops  in  close  relation  to  the  middle  piece  of  the  spermato- 
zoon. These  facts  point  to  the  male  centrosome  as  the  centrosome  of 
fertilization. 

The  o\'um  and  spermatozodn  are  apparently  brought  together  by 
a  definite  attraction  on  the  part  of  the  ovum  toward  the  spermatozoon. 
The  nature  of  this  attraction  is  unknown.  It  is  possibly  chemical, 
and  is  exerted  only  between  ova  and  spermatozoa  of  the  same  species. 
This  has  been  proved  for  lower  forms  by  mixing  ova  of  one  species 
and  spermatozoa  from  se^•eral  species  in  an  inert  medium  when 
only  spermatozoa  of  the  same  species  will  attach  themselves  to  the  ova. 
'i'hat  the  attractive  force  lies  in  the  cytoplasm  is  shown  by  the  fact  that 
small  pieces  of  the  egg  protoplasm  free  from  nuclear  elements  will 
exert  sufficient  attractive  powers  to  cause  spermatozoa  to  enter  them. 


THE  CELL.  57 

As  to  the  point  of  entrance  of  the  spermatozoon,  some  eggs  may 
be  entered  at  any  point,  others  are  permeable  at  but  one  point. 

One  spermatozoon  only  is  required  for  fertilization,  and  when  this 
spermatozoon  has  entered,  the  egg  apparently  loses  its  power  of  at- 
tracting spermatozoa,  or  else  develops  some  actual  defense  against 
further  entrance  of  spermatozoa. 

TECHNIC. 

1.  Fresh  cells  may  be  studied  by  gently  scraping  the  surface  of  the  tongue, 
transferring  the  mucus  thus  obtained  to  a  glass  slide  and  covering  with  a  cover-glass. 

2.  Red  blood  cells  from  the  frog  are  prepared  as  follows:  After  killing  the  frog 
the  heart  is  opened  and  the  blood  allowed  to  drop  into  a  tube  containing  Hayem's 
fluid  (sodium  chlorid  i  gm.,  sodium  sulphate  5  gm.,  mercuric  chlorid  0.5  gm.,  dis- 
tilled water  100  c.c).  After  shaking,  the  cells  are  allowed  to  settle  for  from  twelve 
to  twenty-four  hours.  The  fixative  is  then  replaced  by  water,  the  tube  again 
shaken,  the  cells  allowed  to  settle,  and  the  water  is  replaced  with  80-per-cent.  alco- 
hol tinged  with  iodin.  After  from  twelve  to  twenty-four  hours  the  alcohol  is  de- 
canted and  the  tube  partly  filled  with  alum-carmine  solution  (page  17).  About 
twenty-four  hours  usually  suffices  for  staining  the  nuclei.  The  alum-carmine  is 
then  poured  off  and  the  cells  well  shaken  in  water.  After  settHng,  the  water  is 
replaced  bv  glycerin,  to  which  a  small  amount  of  picric  acid  has  been  added.  In 
this  the  cells  may  be  permanently  preserved.  The  nuclei  are  stained  red  by  the 
carmine,  the  cytoplasm  yellow  by  the  picric  acid. 

3.  Surface  cells  from  the  mucous  membrane  of  the  bladder.  The  bladder  is 
removed  from  a  recently  killed  animal,  pinned  out  mucous  membrane  side  up  on  a 
piece  of  cork  and  floated,  specimen  side  down,  on  equal  parts  ]\Iiiller's  fluid  and 
Ranvier's  alcohol  (technic  4,  p.  6,  and  a,  p.  4)  for  from  twenty-four  to  forty-eight 
hours.  The  specimen  is  then  washed  in  water  and  the  cells  removed  by  gently 
scraping  the  surface.  These  may  then  be  stained  and  preserved  in  the  same 
manner  as  the  preceding.  Cells  from  the  different  layers  should  be  studied;  also 
the  appearance  of  the  large  surface  cells  seen  on  flat  and  on  edge,  showing  pitting 
of  under  surface  by  cells  beneath. 

4.  Amoeboid  movement  may  be  studied  by  watching  fresh-water  amoeba?  or 
white  blood  cells.  A  drop  of  water  containing  amoebae  is  placed  on  a  slide,  covered, 
and  a  brush  moistened  with  oil  is  passed  around  the  cover  to  prevent  evaporation. 
The  activity  of  the  amcebas  may  be  increased  by  slightly  raising  the  temperature. 
An  apparatus  known  as  the  warm  stage  is  convenient  for  demonstrating  amoeboid 
movement.  A  drop  of  blood,  human,  or  better  from  one  of  the  cold-blooded 
animals,  may  be  used  for  the  study  of  amoeboid  movement  in  the  white  blood  cells. 
It  should  be  placed  on  a  slide,  covered,  and  immediately  examined  on  the  warm 
stage. 

5.  Ciliary  movement  is  conveniently  studied  by  removing  a  small  piece  of  the 
gill  of  an  oyster  or  mussel,  teasing  it  gently  in  a  drop  of  normal  salt  solution  and 
covering.  The  cilia  being  very  long,  their  motion  may  be  easily  studied,  especially 
after  it  has  become  slow  from  loss  of  vitalitv. 


58  THE  CELL. 

6.  Mitosis.  The  salamander  tadpole  and  the  newt  are  classical  subjects  for 
the  study  of  cell-division.  The  female  salamander  is  usually  full  of  embryo  tad- 
poles in  January  and  February.  The  embryos  are  removed  and  fixed  in  Flem- 
ming's  fluid  (technic  7,  p.  7),  after  which  they  may  be  preserved  in  equal  parts  of 
alcohol,  glycerin,  and  water.  Mitotic  figures  may  be  found  in  almost  any  of  the 
tissues.  Pieces  of  epidermis  from  the  end  of  the  tail,  the  parietal  peritoneum,  and 
bits  of  the  gills  are  especially  satisfactory.  If  the  newt's  tail  is  used,  it  should  be 
fixed  in  the  same  manner,  embedded  in  parafiin  and  cut  into  thin  sections.  These 
are  stained  with  Heidenhain's  haematoxylin,  technic  3,  p.  16. 

Certain  vegetable  tissues,  such  as  the  end  roots  of  a  young,  rapidly  growing 
onion  or  magnolia  buds,  are  excellent  for  the  study  of  mitosis.  The  technic  is  the 
same  as  for  animal  tissues. 

General  References  for  Further  Study  of  the  Cell. 

Conklin,  E.  G.:  Karyokinesis  and  Cytokinesis.  Jour.  Acad.  Nat.  Sci.  oj  Phila., 
vol.    xii,  1902. 

Harper,  E.  H.:  The  Fertilization  and  Early  Development  of  the  Pigeon's  Egg. 
Amer.  Jour,  oj  Anat.,  vol.  iii,  No.  4,  1904. 

Hertwig,  O.:  Die  Zelle  und  die  Gewebe,  1898. 

Hertwig,  R. :  Eirife,  Befruchtung  u.  Furchungsprozess.  In  Hertwig's  Hand- 
buch  d.  vergleich.  n.  experiment.  Entwickelungslehre  der  Wirbcliiere,  Bd.  I,  Teil  I, 
1903. 

Lillie,  F.  R.:  A  Contribution  toward  an  Experimental  Analysis  of  the  Kary- 
okinetic  Figure.     Science,  New  Series,  vol.  xxvii,  1908. 

McMurrich:  The  Development  of  the  Human  Body. 

Minot:  Human  Embryology.     A  Laboratory  Te.xt-book  of  Embryology. 

Sobotta,  J.:  Die  Befruchtung  u.  Furchung  des  Eies  der  Maus.  Arch.  f.  mik. 
Anat.,  Bd.,  xlv,  1895. 

Wilson,  E.  B.:  The  Cell  in  Development  and  Inheritance,  2d  ed.,  1900. 


PART   III. 
THE   TISSUES. 


CHAPTER  T. 
HISTOGENESIS— CLASSIFICATION. 

Ectoderm,  mesoderm,  and  entoderm  (see  page  56)  are  known 
as  the  primary  layers  of  the  blastoderm.  They  differ  from  one  another 
not  only  in  position,  but  also  in  the  structural  characteristics  of  their 
cells.  The  separation  of  the  blastomeres  into  these  three  layers 
represents  the  first  morphological  differentiation  of  the  cells  of  the 
developing  embryo.  By  further  and  constantly  increasing  differentia  tion 
are  developed  from  these  three  primary  layers  all  tissues  and  organs, 
each  layer  giving  rise  to  its  own  special  group  of  tissues.  The  tissue 
derivations  from  the  primary  layers  of  the  blastoderm  are  as  follows: 

Ectoderm. — (i)  Epithelium  of  skin  and  its  appendages — hair, 
nails,  sweat,  sebaceous  and  mammary  glands,  including  smooth  mus- 
cle of  sweat  glands. 

(2)  Epithelium  of  mouth  and  anus,  of  glands  opening  into  mouth, 
and  enamel  of  teeth. 

(3)  Epithelium  of  nose  and  of  glands  and  cavities  connected  with 
nose. 

(4)  Epithelium  of  external  auditory  canal  and  of  membranous 
labyrinth. 

(5)  Epithelium  of  anterior  surface  of  cornea,  of  conjunctiva,  and 
of  crystalline  lens. 

(6)  Epithelium  of  male  urethra,  except  prostatic  portion. 

(7)  Epithelium  of  pineal  bodies  and  of  pituitary  body. 

(8)  Entire  nervous  system,  including  retina. 

Entoderm. — (i)  Epithelium  of  digestive  tract  excepting  mouth 
and  anus,  and  of  glands  connected  with  digestive  tract. 

(2)  Epithelium  of  respiratory  tract  and  of  its  glands. 

(3)  Epithelium  of  bladder  except  the  trigonum,  of  female  urethra, 
and  of  prostatic  portion  of  male  urethra. 

(4)  Epithelium  of  tympanum  and  of  Eustachian  lube. 

(5)  Epithelium  of  thyreoid  and  of  Hassall's  corpuscles  of  thymus. 
Mesoderm. — (i)  All  the  connective  or  supporting  tissues  except 

neuroglia. 

^      (2)   Lymphatic  organs  with  the  exception  of    Hassall's  corpuscles 
and  reticulum  of  the  thymus. 

(il 


62  THE  TISSUES. 

-''      (3)  Blood  cells  and  bone-marrow. 
^^.       (4)  Striated,  cardiac  and  smooth  muscle  (with  the  possible  excep- 
tion of  smooth  muscle  of  sweat  glands). 
'^      (5)  Endothelium  lining  blood-vessels  and  lymphatics. 

(6)  Mesothelium   lining  serous  membranes — pleura,  pericardium, 
and  peritoneum. 
^      (7)  Epithelium  of  genito-urinary  system  with  the  exception  of  the 
urethra  and  a  large  part  of  the  bladder. 

In  all  but  the  lowest  forms  of  animal  life  the  body  consists  of  an 
orderly  arrangement  of  many  kinds  of  cells.  From  the  cells  is  de- 
veloped a  substance  which  lies  outside  the  cells  and  is  known  as  inter- 
cellular substance.  This  may  be  small  in  amount,  just  sufficient  to 
unite  the  cells,  as  in  epithelium,  or  it  may  so  predominate  as  to  deter- 
mine the  character  of  the  tissue,  as  in  some  forms  of  connective  tissue. 
It  does  not  always  completely  separate  the  cells  which  may  be 
connected  across  the  intercellular  substance  by  extensions  of  their 
protoplasm,  as  in  the  "intercellular  bridges"  of  epithelium  or  the 
anastomosing  processes  of  connective-tissue  cells.  Less  commonly 
cells  are  united  in  such  a  multinuclear  continuum  that  their  boundaries 
are  almost  or  wholly  lost.  Such  a  structure  is  known  as  a  syncytium. 
The  association  of  a  particular  type  of  cell  with  a  particular  type  of 
intercellular  substance  is  known  as  a  tissue.  The  character  of  a  tissue 
depends  upon  the  character  of  its  cells,  of  its  intercellular  substance, 
and  their  relations  to  each  other.  Further  differentiation  of  cells  and 
intercellular  substance  within  a  particular  tissue  gives  rise  to  various 
sub-groups  of  the  tissue.  The  association  of  tissues  to  form  a  definite 
structure  for  the  performance  of  a  particular  function  is  known  as  an 
organ.     The  physiological  association  of  organs  constitutes  a  system. 

A  scientific  classification  of  the  tissues  is  at  present  impossible. 

The  foregoing  list  of  tissue  deri\'ations  shows  how  unsatisfactory 
is  any  attempt  at  classification  on  the  basis  of  histogenesis,  many 
tissues  which  are  morphologically  similar  being  derived  from  two  or 
even  all  three  of  the  blastodermic  layers. 

The  following  is  the  usual  classification  of  adult  tissues:  (i)  Epithe- 
lial tissues;  (2)  connective  tissues;  (3)  blood;  (4)  muscle  tissue;  (5) 
ner\-e  tissue. 

Of  these,  epithelium  and  connective  tissue  may  be  regarded  as  the 
more  elementary  tissues,  being  common  to  both  plants  and  animals. 
Blood  is  sometimes  classified  among  the  connective  tissues.  Muscle  and 
nerve  are  the  most  highly  specialized  tissues  and  are  peculiar  to  animals. 


CHAPTER  II. 

EPITHELIUM   (INCLUDING  MESOTHELIUM  AND 
ENDOTHELIUM;. 

General  Characteristics. — Epithelium  is  derived  from  all  three 
germ  layers.  It  consists  almost  wholly  of  cells.  The  intercellular 
substance  is  merely  sufficient  to  attach  the  cells  to  one  another  and  is, 
consequently,  known  as  cement  substance.  In  some  instances  the 
protoplasm  of  adjacent  epithelial  cells  is  seen  to  be  even  more  closely 
associated,  the  intervening  cement  substance  being  bridged  over  by 
delicate  processes  of  protoplasm  which  pass  from  one  cell  to  another 
and  are  known  as  ^intercellular  bridges''^  (see  Fig.  19,  p.  66).  It  seems 
probable  that  the  minute  spaces  between  the  processes  serve  as  channels 
for  the  passage  of  food  (lymph)  to  the  cells.  The  surface  cells  of 
epithelium  are  united  by  continuous  cement  substance  in  which  there 
are  apparently  no  spaces.     In  this  way  escape  of  lymph  is  prevented. 

Epithelial  cells  vary  in  size  and  shape,  the  element  of  pressure 
being  a  frequent  determining  factor  as  regards  shape.  Their  proto- 
plasm may  be  clear,  finely  or  coarsely  granular,  or  pigmented.  Each 
cell  usually  contains  a  single  well-defined  nucleus.  Two  or  more 
nuclei  are  sometimes  present.  Some  epithelial  cells  are,  when  fully 
matured,  non-nucleated,  e.g.,  respiratory  epithelium  of  lung. 

When  epithelium  rests  upon  connective  tissue,  it  is  usually  sepa- 
rated from  the  latter  by  a  thin,  apparently  homogeneous  membrane 
known  as  the  ha  sal  membrane  or  membra  na  propria.  Authorities 
differ  as  to  whether  this  membrane  is  of  connective-tissue  or  of  epithe- 
lial origin. 

Surface  epithelial  cells  frequently  have  thickened  free  borders  or 
cuticiilcE,  which  unite  to  form  a  continuous  membrane,  the  ciiticiilar 
membrane.  Striations  extend  from  the  cytoplasm  into  the  cuticulae. 
A  still  greater  specialization  of  the  surface  of  the  cell  is  seen  in  the 
ciliated  cell.  In  this  cell  fine  hair-like  projections — cilia — extend 
from  the  surface  of  the  cell. 

Some  epithelial  cells  show  important  changes  dependent  upon 
their  functional    activities.     An  example  of  this  is  seen  in  the  mucous 

03 


(U 


THE  TISSUES. 


cell  in  which  there  is  a  transformation  of  the  greater  part  of  the  cyto- 
plasm into,  or  its  replacement  by,  mucus. 

Epithelia  are  devoid,  as  a  rule,  of  both  blood-  and  lymph-vessels. 
An  exception  to  this  is  the  stria  vascularis  of  the  cochlea.  Nerves, 
on  the  other  hand,  are  abundant. 

Classification. — Epithelia  may  be  classified  according  to  shape 
and  arrangement  of  cells  as  follows: 

(i)  Simple  Epithelium. — (a)  Squamous;  (b)  columnar. 

(2)  Stratified  Epithelium. — (a)  Squamous;  {b)  columnar. 

(3)  Mesothelium  and  Endothelium. 

Specializations  of  the  above-mentioned  types  are  known  as :  (a) 
Ciliated  epithelium;  (b)  pigmented  epithelium:  (c)  glandular  epithe- 
lium; (d)  neuro-epithehum. 

Pigment  may  occur  in  any  type  of  epithelium.  Cilia  are  found 
only  in  the  simple  columnar  and  stratified  columnar  forms. 


I.  Simple  Epithelium. 

In  simple  epithelium  the  cells  are  arranged  in  a  single  layer. 
(a)   Simple   squamous   epithelium   consists    of   fiat    scale-like    cells 
which  are  united  by  an  extremely  small  amount  of  intercellular  sub- 


FiG.  15. — From  Section  of  Cat's  Lung,  stained  with  silver  nitrate,  showing  outlines  of 
the  Simple  Squamous  Epithelium  Lining  the  Air  Vesicle,  a,  Two  epithelial  cells;  h,  the 
wavy  staincfl  intercellular  substance;  c,  foetal  cells;  d,  connective  tissue. 

Stance.  The  edges  of  the  cells  are  smooth  or  serrated.  Seen  on 
flat,  they  present  the  appearance  of  a  mosaic.  Seen  on  edge,  the 
cells  appear  fusiform,  being  thickest  at  the  centre,  where  the  nucleus 


EPITHELIUM. 


65 


is  situated,  and  thinning  out  toward  the  periphery.  Simple  squa- 
mous epithehum  has  but  a  limited  distribution  in  man.  It  occurs 
in  the  lungs  as  non-nucleated  respiratory  epithelium,  in  Bowman's 
capsule  of  the  renal  corpuscle,  in  the  descending  arm  of  Henle's  loop 
of  the  uriniferous  tubule,  in  the  retina  in  the  form  of  pigmented  cells, 
and  on  the  posterior  surface  of  the  anterior  lens  capsule. 


iS 


-m 


■j  ■'*■  ■ 


-H d 


:iiiiBifii:#PII 


Fig.  i6. — Simple  Columnar  Epithelium  from  the  Human  Small  Intestine,  a,  Mucous 
(goblet)  cell;  b,  basement  membrane;  c,  thickened  free  border  (cuticula);  d,  leucocyte 
among  the  epithelial  cells;  e,  replacing  cell. 


(b)  Simple  columnar  epithelium  consists  of  a  single  layer  of  elon- 
gated cells.  The  bases  of  the  cells  are  usually  separated  from  the 
underlying  connective  tissue  by  a  basement  membrane.  The  nu- 
cleus is,  as  a  rule,  in  the  deeper  part  of  the  cell,  near  the  basement 
membrane.  Many  of  these  cells  have  prominent  thickened  free 
borders  or  cuticulae.  This  form  of  epithelium  is  often  ciliated.  The 
height  of  the  cell  varies  greatl3^  there  being  all  gradations  from  high 
columnar  to  low  cuboidal.  Simple 
columnar  epithelium  lines  the  gastro- 
intestinal canal,  the  uriniferous  tubule 
(excepting  the  descending  arm  of 
Henle's  loop),  simple  tubular  glands, 
the  ducts  of  some  compound  tubular 
glands,  the  smaller  bronchi,  the  mem- 
branous and  penile  portions  of  the 
male  uretha,  and  the  gall-bladder. 

In  simple  columnar  epithelium,  in  addition  to  the  single  row  of 
epithelial  cells,  there  are  found  lying  near  the  basement  membrane, 
between  the  bases  of  the  epithelial  cells,  small,  spherical,  or  irregular 
cells,  which  frequently  show  mitosis  and  which  are  known  as  replacing 
cells.  They  appear  to  develop  into  columnar  epithelial  cells  as  they 
are  needed  to  replace  older  cells.  The  so-called  pseudo-stratijied 
5 


Fig.  17. — Diagram  of  Pseudosiraliried 
Epithelium,  showing  Nuclei  situated 
at  Different  Levels. 


66 


THE  TISSUES. 


epitJielium  is  a  form  of  simple  columnar  epithelium,  in  which,  from 
crowding  of  the  cells,  the  nuclei  have  come  to  lie  at  different  levels, 
thus  giving  the  appearance  of  stratification  (Fig.  17). 

2.  Stratified  Epithelium. 

In  stratified  epithelium  the  cells  are  arranged  in  more  than  one 
layer. 


Flat  surface  cells 


;^^S'":r;: 


.<^'  % 


Polyhedral  cells  '.  <^_i2 


1^ 


,«si,      ^        'm 


r^ 


m 


-^w 


Cuboidal  cells 


Fig.   18. — Stratified  Squamous  Epithelium  from  Cat's  (Esophagus. 

(a)  Stratified  squamous  epithelium  is  developed  from  simple  epithe- 
lium by  the  growth  of  new  cells  between  the  old  cells  and  the  under- 
lying connective  tissue.      It  consists  of  several 
f)^^j^-ai$^ (ji'^-^^t^^     layers  of  cells  which  vary  greatly  in  size  and 
shape.      The  surface  cells  are  large  and  flat. 
Beneath  these  are  several  layers  of  polyhedral 
cells,    with   often    very    distinct   protoplasmic 
intercellular    connections    ("intercellular 
bridges,"   see    also   page    63).      The   deepest 
cells    are  columnar  or  cuboidal.       It  is  thus 
seen   that   in   stratified  squamous  epithelium 
only  the  surface  cells  are  sc[uamous.      This 
from  ihe  Stratum  Spinosum    f^j-j^  Qf  epithelium  rcsts  upou  a  more  or  less 

of    the    Human  Epidermis 

showing     "Intercellular    distinct   basement   membrane,    which   is  fre- 

monowifz )      ^°°       ^'^"    'I'-'^^tly  thrown    up  into   folds    l)y   papillae  of 

the   underlying  connecti\e  tissue.      Stratified 

squamous     epithelium     forms     the     surface     of    the    skin     and    of 

mucous  membranes  of  cavities  opening  upon  it,  mouth  and  cesoph- 


u 


"M 


V\<:.      ig. — Epithelial      Ctlls 


EPITHELIUM. 


6/ 


agus,   conjunctiva,  external   ear,  vagina,  and  external  sheath  of  hair 
follicle. 

(b)  Stratified  Columnar  Epithelium. — Only  the  surface  cells  are 
columnar,  the  deeper  cells  being  irregular  in  shape.  The  surface 
cells  frequently  send  long  processes  down  among  the  underlying 
cells.     The  free  surface  is  often  marked  by  a  well-developed  cuticula. 


CD 


%^  mM 


Fig.   20. — Transitional  Epithelium  from  the  Human  Bladder. 

Some  epithelia  of  this  type  are  ciliated.  Stratified  columnar  epithe- 
lium is  found  in  the  larynx,  nose,  palpebral  conjunctiva,  largest  of 
the  gland  ducts,  the  vas  deferens,  and  part  of  the  male  urethra. 

Stratified  epithelium  composed  of  only  from  three  to  six  layers 
of  cells  is  sometimes  designated  '"transitional  epithelium^  This 
type  of  epithelium  usually  rests  upon  a  basement  membrane  free  from 


Fig.   21. — Stratified  Columnar  Epithelium  from  the  Human   Male  I'rethra.      X400. 


papillse.  The  surface  cells  are.  large  and  frequently  contain  two  or 
three  nuclei.  Their  free  surfaces  are  flat,  while  their  under  surfaces 
show  depressions  due  to  pressure  from  underlying  cells.  The  deeper 
cells  arc  polygonal  or  irregularly  cuboidal.  Tliis  form  of  epithelium 
lines  the  bladder,  ureter,  pehis  of  the  kidney,  and  prostatic  portion 
of  male  urethra. 


68 


the  tissues. 
Modified  Forms  of  Epithelium. 


(a)  Ciliated  Epithelium. — In  this  form  of  epithelium,  fine  hair-like 
processes — cilia — extend  from  the  surface  of  the  cell.  These  cilia 
vary  from  twelve  to  twenty-five  for  each  cell  and  may  be  short  as  in  the 


Si;'  ^- 


c 


a;     ^    -'^       '^' 


W 


^ 


#i 


^ 


n 


Fig.    22. — Stratified    Columnar    Ciliated    Epithelium    from    the    Human    Trachea.      A 
mucous  (goblet)  cell  also  is  present. 

trachea  or  long  as  in  the  epididymis.  There  is  usually  a  well-defined 
cuticula  from  which  the  cilia  appear  to  spring.  According  to  Apathy, 
the  cilia  extend  through  the  cuticula,  giving  to  the  latter  a  striated 


Fig.   23. — Isolated  Ciliated  Cells  and  Goblet  Cells  from  Dog's  Trachea.      X700. 

appearance  (Fig.  24).  Just  beneath  the  cuticula  each  cilium  shows 
a  swelling — the  basal  granule.  Lenhossek  considers  these  granules 
centrosomes.     The    intracellular     extensions    of    the    cilia    converge 


EPITHELIUM. 


69 


toward  the  nucleus,  and  are  continuous  with  the  reticular  or  fibrillar 
structure  of  the  cell  body.  The  motion  of  cilia  is  wave-like,  the  wave 
always  passing  in  the  same  direction.  Various  explanations  of  ciliary 
motion  have  been  given.  The  most  plausible  is  that  it  is  due  to  the 
contractile  powers  of  the  spongioplasm. 

Cilia  are  confined  to  the  surface  cells  of  simple 
columnar  and  stratified  columnar  epithelium. 

Simple  columnar  cihated  epithelium  occurs  in 
the  smaller  bronchi,  uterus,  Fallopian  tubes  and 
central  canal  of  the  spinal  cord. 

Stratified  clumnar  ciliated  epithelium  occurs  in 
large  bronchi,  trachea,  larynx,  nose.  Eustachian 
tube,  vas  deferens  and  epididymis. 

(b)  Pigmented  epithelium  consists  of  cells  the 
cytoplasm  of  which  contains  brown  or  black  pig- 


FiG.   24.  Fig.   25. 

Fig.  24.— Ciliated  Epithelial  Cell  from  Intestine  of  Mollusk  (Engelmann),  showing,  a, 
cuticula,  b,  basal  granules,  and  c,  intracellular  extensions  of  cilia. 

Fig.  25.— Pigmented  Epithelial  Cells  from  the  Human  Retina  (X350),  showing  dif- 
ferent degrees  of  pigmentation.  The  clear  spots  in  the  centres  of  the  cells  represent  the 
unstained  nuclei. 

ment.  It  is  usually  present  in  the  form  of  spherical  or  rod-like  granules. 
Examples  of  it  are  seen  in  the  pigmented  epithelium  of  the  retina  and 
in  the  pigmented  cells  of  the  deeper  layers  of  the  epidermis  in  colored 
races  (Fig.  25). 

(c)  Glandular  Epithelium.— This  forms  the  essential  or  secreting 
element  of  glands  and  is  mostly  of  the  simple  cylindrical  \ariety. 
The  dift'erent  kinds  of  glands  and  their  epithelia  will  be  described 
among  the  organs. 

(d)  Neuro-epithelium. — This  is  a  highly  specialized  form  of  epithe- 
lium which  occurs  in  connection  with  the  end  organs  of  ner^■es.  under 
which  heading;  it  will  be  described. 


70 


THE  TISSUES. 


3.  Mesothelium  and  Endothelium. 

While  recognizing  the  present  tendency  toward  considering  those 
tissues  formerly  classified  as  endothelium,  as  simple  squamous  epithe- 
lium, the  correctness  of  the  newer  classification  still  remains  sub  judice 


Fig.  26. — Mesothelium  from  Omentum  of  Dog  Treated  according  to  Technic  7,  p.  j?. 
X350.  Black  wavy  lines  indicate  the  intercellular  cement  substance.  The  mesothelial 
cells  cover  the  strands  of  connective  tissue,  the  fibres  of  the  latter  being  visible  through  the 
transparent  cell  bodies. 

and,  so  long  as  this  is  the  case,  we  prefer  to  retain  the  certainly  much 
more  convenient  classification  of  Minot,  which  coincides  with  his 
subdivision  of  the  mesoblast.  According  to  this  classification,  for 
those  tissues  which  resemble  epithelium  in  structure  and  which  are 
derived  from  the  sublayer  of  the  mesoderm  which  he  designates  the 


Fig.    27. — The  J'.ndothcliuin  of  a  Small  Ijlood-vessel.     Silver  nitrate  stain.      X350. 


mesenchyme,  the  term  endothelium  is  retained.  The  term  mesothelium 
is  used  for  those  tissues  which  rescm1)Ie  epithelium  but  arc  derived 
from  a  subdi\'ision  of  the  mesoderm  which  he  designates  tiie  meso- 
thch'al  layer. 


EPITHELIUM.  / 1 

Mesothelium  and  endothelium  are  similar  in  structure.  Each 
consists  of  thin  flattened  cells  with  clear  or  slightly  granular  proto- 
plasm and  bulging  oval  or  spherical  nuclei.  The  edges  of  the  cells 
are  usually  wa\  y  or  serrated.  The  cells  are  united  by  an  extremely 
small  amount  of  intercellular  "cement"  substance,  which  is  usually 
indistinguishable  except  by  the  use  of  a  special  technic. 

Endothelium  forms  the  walls  of  the  blood  and  lymph  capillaries 
and  lines  the  entire  blood-vessel  and  lymph-vessel  systems. 

Mesothelium  lines  the  body  cavities — the  pleura,  the  pericardium, 
and  the  peritoneum. 

TECHNIC. 

1.  Simple  Squamous  Epithelium. — That  of  the  lung  may  be  demonstrated  by 
injecting  with  silver  solution  (technic  i,  p.  26)  through  a  bronchus  and  then  im- 
mersing the  tissue  in  the  same  solution.  The  lungs  of  young  kittens  furnish  espe- 
cially satisfactory  material. 

2.  Simple  Columnar  Epithelium. — A  piece  of  small  intestine,  human  or  animal, 
is  pinned  out  flat  on  cork  and  fixed  in  formaHn-^NIiiller's  fluid  (technic  5,  p.  7). 
Sections  are  cut  perpendicular  to  the  surface,  stained  with  hematoxylin  and  eosin 
(technic  i,  p.  18)  and  mounted  in  glycerin  tinged  with  eosin  (page  20).  Little 
processes  known  as  villi  project  from  the  inner  surface  of  the  intestine.  These 
are  covered  by  a  single  layer  of  columnar  epithelial  cells.  The  cuticulte  and 
cuticular  membrane  are  usually  well  shown.  Among  the  simple  cylindrical  cells 
are  seen  large  clear  or  slightly  blue-stained  cells.  These  are  known  from  their 
secretion  as  mucous  cells,  from  their  shape  as  goblet  cells,  and  are  classed  as 
modified  epithelium  of  the  glandular  type.  These  should  be  studied  in  their  va- 
rious stages  of  secretion,  from  the  cell  in  which  only  a  small  amount  of  mucus  is 
present  near  the  outer  margin,  to  the  cell  whose  protoplasm  is  almost  wholly  re- 
placed by  mucus.  Some  cells  will  be  found  in  which  the  surface  has  ruptured  and 
the  mucus  can  be  seen  pouring  out  of  the  cell. 

3.  Stratified  Squamous  Epithelium. — The  cornea  furnishes  good  material  for 
the  study  of  stratified  squamous  epithelium.  An  eye  is  removed  from  a  freshly 
killed  animal  and  the  cornea  cut  out  and  fixed  in  formalin-Miiller's  fluid.  Sections 
are  cut  perpendicular  to  the  surface,  and  treated  as  in  the  preceding.  The  cells 
are  laid  down  in  from  six  to  eight  layers.  The  cesophagus  may  be  used  instead  of 
the  cornea,  its  mucous  membrane  being  lined  by  a  somewhat  thicker  epithelium. 

4.  Transitional  Epithelium. — This  is  conveniently  studied  in  the  mucous  mem- 
brane of  the  bladder.     Technic  same  as  2,  above. 

5.  Stratified  Columnar  Epithelium. — A  portion  of  trachea  from  a  recently 
killed  animal  is  treated  according  to  the  same  technic.  The  surface  cells  arc  ciliated 
so  that  this  specimen  also  serves  to  demonstrate  that  type  of  modified  ej)ithclium. 
Isolated  cells  or  clumps  of  cells  may  be  obtained  from  the  trachea  in  the  manner 
described  in  technic  3,  p.  57. 

6.  Pigmented  Epithelium. — Fix  a  freshly  removed  eye  in  lormalin-Muller's 
fluid  (page   7).     After  hardening,  cut  transversely  and  remove  the  vitreous  and 


72  THE  TISSUES. 

retina.  The  pigmented  cells  remain  attached  to  the  inner  surface  of  the  chorioid, 
and  may  be  removed  by  gently  scraping.  They  may  be  preserved  and  mounted  in 
glycerin. 

7.  Mesothelium. — Part  of  the  omentum  of  a  recently  killed  animal  is  removed 
and  washed  in  water,  care  being  taken  not  to  injure  the  tissue  in  handling.  The 
water  is  then  replaced  by  a  i  to  500  aqueous  solution  of  silver  nitrate.  After  half 
an  hour  the  specimen  is  removed  from  the  silver,  washed  in  water,  transferred  to 
80-per-cent.  alcohol  and  placed  in  the  sunlight  until  it  becomes  light  brown  in 
color.  It  is  then  preserved  in  fresh  80-per-cent.  alcohol.  The  nuclei  may  be 
stained  with  haematoxylin  (stain  5,  p.  16).  The  specimen  should  be  mounted  in 
glycerin.  Wavy  black  lines  indicate  the  intercellular  cement  substance.  The 
nuclei  of  the  mesothelial  cells  are  stained  blue,  those  of  the  underlying  connective- 
tissue  cells  a  paler  blue.  It  must  be  borne  in  mind  in  studying  this  specimen  that 
the  strands  or  trabeculas  of  the  omentum  are  not  composed  of  mesothelium,  but  of 
fibrous  connective  tissue,  and  that  the  flat  mesothelial  cells  merely  lie  upon  the 
surface  of  the  connective-tissue  strands. 

8.  Endothelium  may  be  demonstrated  by  removing  the  bladder  from  a  recently 
killed  frog,  distending  it  with  air  and  subjecting  it  to  the  same  technic.  By  this 
means  the  intercellular  substance  of  the  endothelium  of  the  blood-vessels  of  the 
bladder  wall  is  stained  and  the  outlines  of  the  cells  are  thus  shown. 


CHAPTER  III. 
THE  CONNECTIVE  TISSUES. 

General  Characteristics. — All  of  the  connective  tissues,  with  the 
single  exception  of  the  connective  tissue  peculiar  to  the  nervous  system 
(neuroglia),  are  developed  from  the  mesoderm.  This  consists  at  first 
wholly  of  round  or  polygonal  cells  united  by  a  small  amount  of  inter- 
cellular cement  substance.  As  development  proceeds  the  cells  gradu- 
ally become  more  and  more  separated  from  one  another  by  an  increased 
amount  of  intercellular  substance.  This  intercellular  substance  is  a 
product  of  the  cells  and  is  at  first  homogeneous  or  granular.  The 
appearance  presented  at  this  stage  is  that  of  irregular,  branching, 
anastomosing  cells,  lying  in  a  semi-fluid  ground  substance.  This  is 
embryonic  connective  tissue.  With  further  changes  in  both  cells  and 
intercellular  substance,  but  mainly  in  the  latter,  embryonic  connective 
tissue  differentiates  to  form  the  adult  types  of  connective  tissue. 

The  most  prominent  characteristic  of  the  connective  tissues,  with 
the  exception  of  adenoid  tissue  and  fat,  is  the  predominance  of  the 
intercellular  substance.  In  this  respect  the  connective  tissues  differ 
markedly  from  epithelial  tissues  and  this  difference  in  structure  cor- 
responds to  difference  in  function.  The  role  which  the  connective 
tissues  play  is  mainly  passive,  and  the  cells  instead  of  taking,  as  in 
epithelium,  muscle  and  nerve  tissues,  the  most  active  part,  serve  mainly 
for  the  maintenance  of  the  nutrition  of  the  more  important  inter- 
cellular substance.  Moreover,  with  the  exceptions  mentioned  above,  it 
is  the  intercellular  substance  and  not  the  cells  which  determines  the 
physical  character  of  the  tissue.  The  denser  forms  of  connective  tissue, 
such  as  bone  and  cartilage,  are  supportive  in  function;  somewhat  less 
dense  tissues,  such  as  tendons,  serve  to  attach  muscles  to  bones;  while 
more  loosely  arranged  connective  tissue  forms  the  frame-work  of  the 
various  organs.  Connective  tissue  differs  also  from  epithelium  as  re- 
gards its  blood  supply,  being  usually  though  not  always  very  vascular. 
A  further  characteristic  of  the  connective  tissues  is  the  apparent  ease 
with  which  one  type  may  become  transformed  into  another. 

The  division  of  connective  tissue  into  its  various  sub-groups  is  also 
based  upon  structural  dift'erences  in  the  intercellular  substances. 

73 


74  THE  TISSUES. 

Classification. — The  connective  tissues  may  be  classified  as  follows, 
although  embryonal  tissue  and  mucous  tissue  are  essentially  develop- 
mental forms. 

1.  Fibrillar  connective  tissue,  including  areolar  tissue. 

2.  Elastic  tissue. 

3.  Embryonal  tissue  and  mucous  tissue. 

4.  Reticular  tissue. 

c;.  Lymphatic  or  adenoid  tissue. 

6.  Fat  tissue. 

[  (a)   Hyaline. 

7.  Cartilage.    \  (b)  Elastic. 

[  (c)  Fibrous. 

8.  Bone  tissue. 

9.  Neuroglia. 

I.  Fibrillar  Connective  Tissue. 

Fibrillar  connective  tissue,  also  known  as  white  fibrous  tissue  or 
connective  tissue  proper,  consists  of  cells  and  fibres  lying  in  a  basement 
or  ground  substance.  The  elements  of  fibrillar  tissue  may  be  classified 
as  follows: 

[     (a)  The    ordinary  connective-tissues   cells. 
[     I.  Fixed    \     (b)  Plasma  cells. 
Cells     ]  [    (c)  Mast  cells. 


2.  Wanderino;. 


Intercellular    substance. 


^.,  white    or    fibrillated, 

(a)  Fibres  ,,  ,     .. 

^  ^  yellow    or    elastic. 


[  (b)  Ground  or  basement  substance. 
Connective-tissue  Cells.— (a)  The  ordinary  fixed  connective-tissue 
cellh  often  the  only  connective-tissue  cell  seen  in  ordinary  sections. 
It  is  a  flat,  irregularly  stellate  cell  with  many  branches  (Fig.  30).  The 
nucleus  lies  in  the  thickest  part  of  the  cell.  The  cytoplasm  is  usually 
clear  or  slightly  granular.  Each  cell  lies  in  a  cell  space  or  lacuna. 
From  the  cell  spaces  minute  channels  {canaliculi)  extend  in  all  direc- 
tions to  unite  with  canaliculi  from  adjoining  spaces  (Fig.  29).  Delicate 
cell  processes  extend  into  the  canaliculi  and  there  anastomose  with 
processes  from  other  cells  (Fig.  30).  Owing  to  the  extreme  sensitive- 
ness of  the  protoplasm  of  the  connective-tissue  cell  to  most  fixatives,  its 
usual  appearance  is  that  of  a  minute  amount  of  cytoplasm  shrunken 
down  around  a  nucleus. 


THE  CONNECTIVE  TISSUES. 


(b)  Plasma  Cells. — These  cells  occur  mainly  near  the  smaller  blood- 
vessels. Their  protoplasm  is  finely  granular  and  stains  with  basic 
aniline  dyes.  They  frequently  contain  vacuoles.  Small  plasma  cells 
are  about  the  size  of  leucocytes,  which  they  closely  resemble.  Large 
plasma  cells  are  larger  than  leucocytes  and  richer  in  protoplasm. 
Some  consider  them  as  derived  from  leucocytes,  others  as  a  modified 
form  of  the  ordinary  fixed  connective-tissue  cell. 

(c)  Mast  cells  are  spherical  or  irregular-shaped  cells,  found  like 
the  preceding  in  the  neighborhood  of  the  blood-vessels.     Their  proto- 


FiG.  28. — Fibrillar  Connective  Tissue  (Areolar  Type)  from  Subcutaneous  Tissue  of 
Rabbit  (technic  2,  p.  80).  X500.  a,  Fixed  connective-tissue  cell;  b,  fibrillated  fibres;  c 
elastic  fibre  with  curled  broken  end;  d,  elastic  fibres  showing  Y-shaped  branching. 

plasm  contains  coarse  granules  which  stain  intensely  with  basic  aniline 
dyes.  They  are  believed  by  some  investigators  to  be  connected  with 
the  formation  of  fat;  by  others  to  represent  a  stage  in  the  development 
of  the  fixed  connective-tissue  cell. 

Connecti\'e-tissue  cells  may  be  pigmented  (Fig.  31).  In  such 
cells  the  cytoplasm  is  more  or  less  filled  with  brown  or  black  pigment 
granules.  In  man  pigmented  connecti^■e-tissue  cells  occur  in  the  skin, 
chorioid  and  iris. 

The  so-called  icandering  cells  are  not  properly  a  part  of  connective 
tissue,  being  merely  amoeboid  white  blood  cells  (see  page  98)  which 
ha\-e  passed  out  from  the  \essel  into  the  tissues.  Tliey  are  not  peculiar 
to  conncctiN'c  tissue,  being  found  in  other  tissues,  Ci^..  in  ejiitlKlium. 


76  THE  TISSUES. 

The  Intercellular  Substance. — (a)  Fibres.  White  or  fibrillated 
^^f^"^  are  bundles  of  extremely  fine  fibrillse  (o.  5 /«  in  diameter)  (Fig.  28). 
The  fibrillae  lie  parallel  to  one  another  and  are  united  by  a  small  amount 
of  cement  substance.     The  fibrillae  do  not  branch.     The  fibre  bundles, 

*?KJ''?^<3?S  ;-      ■  •■-,  ■■  ■ 


.^cT^' 


■'.  '     ■■  "^  V.  ■  ■■,■•-■-.,.1-::/:;  ;  -^^ ■■".■. .:;;::.3:# 

Fig.  29. — Section  of  Human  Cornea  cut  Tangential  to  Surface.  X  350.  (Technic  g, 
p.  81.)  Connective-tissue  Cell  Spaces  (Lacunae)  and  Anastomosing  Canaliculi,  white; 
whole  Intercellular  Substance  (Ground  Substance  and  Fibres),  dark. 

on  the  other  hand,  branch  dichotomously  and   anastomose.     White 
fibres,  on  boiling,  yield  gelatin. 

Yellow  or  elastic  fibres  are  apparently  homogeneous,  highly  re- 
fractive fibres,  varying  in  diameter  from  i  to    lo/i  (Fig.  28).     They 


~W.,??"'T".' 


'\  /  /■■'" 


Fig.  30. — Section  of  Human  Cornea  cut  Tangential  t©  Surface.  X  350.  (Technic 
8,  p.  81.)  Connective-tissue  Cells  with  Anastomosing  Processes,  stained;  Intercellular 
Substance  (Ground  Substance  and  P'ibres),  unstained. 

branch  and  anastomose,  forming  networks.  The  smaller  fibres  are 
round  on  cross  section,  llie  larger  flattened  or  hexagonal  (Figs,  t,^ 
and  34j.  Their  elasticity  is  easily  demonstrated  in  teased  specimens 
by  curling  of  the  broken  ends  of   the  fibres    (Fig.  28).     On   boiling 


THE  COXXECTI\-E  TISSUES. 


they  yield  elastin.  Although,  when  subjected  to  the  usual  technic, 
elastic  fibres  appear  homogeneous,  they  are  probably  composed  of  a 
thin  sheath  or  membrane,  enclosing  the  more  granular  elastin.  The 
latter  stains  intensely  with  magenta,  the  sheath  remaining  unstained. 
In  addition  to  the  white  v^^::--:"-.:;. 


Wa^SS^ 


Fig.  31. — Pigmented  Connective-tissue  Cells  from 
Chorioid  Coat  of  Human  Eye.  X  350.  (Technir 
7,  p.  81.) 


fibres  and  elastic  fibres 
above  described,  so-called 
"reticular"  fibres  are  fre- 
quently present  in  fibril- 
lated  connective  tissue. 
(See  p.  83.) 

(b)  Basement  or  ground 
substance  occurs  in  ex- 
tremely minute  amounts 
between  the  individual 
fibrilte  of  the  white  fibres,  where  it  acts  as  a  cement  substance.  The 
same  material  also  forms  the  basement  or  ground  substance  in  which 
the  connective-tissue  cells  and  fibres  lie  (Fig.  29).  Difficulty  in  seeing 
this  ground  substance  is  due  to  its  transparency.  It  may  be  demon- 
strated by  staining  with  silver  nitrate.      (See  technic  9,  p.  81.) 

Much  variation  exists  in  regard  to  the  proportions  of  the  different 
elements.  This  gives  rise  to  variations  in  the  physical  characteristics 
of  the  tissue.     When  fibres  predominate  over  cells  and  ground  sub- 

stance,  the  tissue  is  dense  and 

'^^^x^v  ^  _'  ^*  ,.-^^,     hard  and  is  known  as  dense 

<??^;  ""'-'■'  -  fibrous   tissue.       The    terms 

rT;.:     ' .,  "  V  -        -:\-      fine   connective    tissue    and 

:;  '  '  f  oa;'5(?  connective  tissue  desig- 

^_-  _  ,  J     '         ^-  ;      nate    the    character   of   the 

■  -    ~  '      -  fibres.     When  many  cells  are 

^  \  ,    ,„  present,  the  tissue  is   softer 

s"r--  -    ^    -:■-    _     -;   -    -         and  is  known  as  cellular  con- 

nective tissue. 

According  to  the  arrange- 
ment   of    the    wliite    fibres, 
fibrous    connective   tissue  is 
subdivided  as  follows: 

(i)  Areolar  or  Loose  Connective  Tissue. — In  this  the  fibres 
are  irregular,  running  in  all  directions  and  interlacing,  leaving  between 
them  meshes  or  areola'  (Fig.  28). 


Fig.  32. — Longitudinal  Section  of  Tendon  from 
Frog's  Gastrocnemius.  X  250.  The  nuclei  of 
the  flattened  cells  are  seen  lying  in  rows  between 
the  connective-tissue  fibres. 


78  THE  TISSUES. 

Subcutaneous  connective  tissue  is  a  typical  example  of  areolar 
tissue.  Both  white  and  elastic  fibres  are  present,  although  the  former 
predominate.  Areolar  tissue  varies  greatly  as  regards  the  relative 
number  of  cells  and  fibres  and  the  closeness  with  which  the  different 
elements  are  packed.     It  thus  varies  greatly  in  density. 

(2)  Formed  Connective  Tissue. — In  this  the  fibres  all  run  in 
approximately  the  same  direction,  and  are  united  by  a  small  amount 
of  ground  substance  (Fig.  32).  There  are  but  few  cells  and  these  are 
flattened  out  by  pressure  and  lie  between  the  fibres,  their  long  axes  cor- 
responding to  the  direction  of  the  fibres.  This  arrangement  of  tissue 
elements  forms  a  firm,  dense  tissue,  such  as  is  found  in  tendons  and 
ligaments.  Formed  connective  tissue  also  occurs  as  anastomosing 
networks  of  fibres,  as,  e.g.,  in  the  omentum  (page  235).  It  should  be 
noted  that  between  dense  "formed"  connective  tissue  on  the  one  hand 
and  loose  "areolar"  tissue  on  the  other,  all  gradations  exist. 

Regarding  the  development  of  the  connective-tissue  fibrils,  there  are  two 
theories:  (i)  According  to  one,  they  are  developed  directly  from  the  protoplasm  of 
the  connective-tissue  cells.  The  cells  increase  in  length,  and  fine  granules  appear, 
which  arrange  themselves  in  rows  in  the  cytoplasm;  these  granules  unite  to  form 
fibrils.  Such  cells  are  known  as  fibroblasts,  and  their  fibrils  are  the  forerunners  of 
the  intercellular  fibrils  of  connective  tissue.  A  modification  of  this  theory  derives 
the  fibrils  from  the  peripheral  portion  of  the  cell — the  exoplasm.  (2)  According 
to  the  other  theory  the  fibrils  are  developed  from  the  matrix,  minute  granules 
first  becoming  arranged  in  rows  and  later  uniting  to  form  fibrils. 

Regarded  as  opposing  theories,  there  is  in  reality  but  little  antagonism  between 
them.  There  is  no  doubt  as  to  the  intercellular  matrix  being  a  product  of  the  cell. 
Whichever  theory,  therefore,  is  accepted,  the  entire  intercellular  substance,  fibres 
and  ground  substance  are  ultimate  derivatives  of  the  cell.  Recent  studies,  especially 
those  of  Mall,  are  confirmatory  of  the  second  of  the  theories  given  above.  He 
maintains  that  the  connective-tissue  fibrils,  both  white  and  elastic,  are  derivatives 
of  an  active  intercellular  matrix,  which  latter  is  a  direct  product  of  the  cell. 

Two  similar  theories  exist  as  to  the  development  of  elastic  fibres,  a  cellular 
theory  and  an  extracellular  theory.  According  to  some  advocates  of  the  cellular 
theory,  the  elastic  fibres  are  derived  from  the  exoplasm;  according  to  others,  from 
the  cytoplasm  immediately  surrounding  the  nucleus.  Recent  researches  favor 
the  extracellular  theory.  Mall  describes  extremely  minute  fibrils  in  the  ground  sub- 
stance, which  later  develop  into  elastic  fibres. 

2.  Elastic  Tissue. 

Elastic  fibres  occurring  in  fibrous  connective  tissue  have  been  de- 
scribed. When  the  elastic  fibres  predominate  the  tissue  is  known  as 
elastic  tissue.     Almost  pure  elastic  tissue  is  found  in  the  ligamentum 


THE  CONNECTIVE  TISSUES. 


nuchas  of  quadrupeds.  Here  the  fibres  are  coarse  and  held  together 
by  a  small  amount  of  cement  substance.  A  few  white  fibres  and 
connective-tissue  cells  are  also  present  (Figs.  t,t,  and  34). 


Fig.   t^t,. — Coarse  Elastic  Fibres  from  Ligamentum  Nucha;.      X500.     Teased  specimen. 

(Technic  10,  p.  8r). 

Elastic  tissue  may  be  arranged  as  thin  membranes,  as,  e.g.,  in  the 
walls  of  blood-vessels.  These  membranes  are  usually  described  as 
composed  of  a  dense  mass  of  flat,  ribbon-like  elastic  fibres,  which  inter- 


Fig.  34. — Cross  Section  of  Coarse  Elastic  Fibres  from  Ligamentum  Nucha-.  X5C0, 
(Technic  10,  p.  81.)  a.  Elastic  fibres;  h,  while  fibrous  tissue  and  cement  substance.  The 
nuclei  are  the  nuclei  of  fixed  connective-tissue  cells. 

lace  in  such  a  manner  as  to  leaxc  openings  in  the  memljranc.  Hence 
the  term  "  fenestrated  membrane."  They  have  been  recently  described 
as  consisting  of  a   central   layer  composed   of   clastin.   staining  with 


80  THE  TISSUES. 

magenta,  and  on  either  side  a  thin,  transparent  sheath  unstained  by 
magenta.  This  is  seen  to  correspond  to  Mall's  description  of  the 
structure  of  the  elastic  fibre.  Only  the  middle  of  these  layers  is 
fenestrated. 

TECHNIC. 

1.  Areolar  Tissue,  to  show  White  and  Elastic  Fibres. — Remove  a  bit  of  the 
subcutaneous  tissue,  as  free  from  fat  as  possible,  from  a  recently  killed  animal. 
Place  it  upon  a  mounting  slide  and  with  teasing  needles  quickly  spread  it  out  in 
a  thin  layer.  During  this  manipulation  the  specimen  should  be  kept  moist  by 
breathing  on  it.  Put  a  drop  of  sodium  chlorid  solution  upon  the  specimen  and 
cover. 

As  the  specimen  is  unstained,  a  small  diaphragm  should  be  used  for  the  micro- 
scopic examination. 

The  white  fibres  are  straight  or  wavy,  are  crossed  in  all  directions,  and  are 
longitudinally  striated.  The  elastic  fibres  have  been  stretched  and  show  as  sharp 
lines  with  curled  ends  where  the  fibres  are  broken. 

Place  a  drop  of  hydric  acetate,  i-per-cent.  aqueous  solution,  at  one  side  of  the 
cover  and  a  bit  of  filter  paper  at  the  other  side.  The  filter  paper  absorbs  the  salt 
solution,  which  is  replaced  by  the  hydric  acetate.  The  latter  causes  the  white 
fibres  to  swell  and  become  indistinct  while  the  elastic  fibres  show  more  plainly. 

2.  Areolar  Tissue,  to  show  Cells  and  Elastic  Fibres. — Prepare  second  specimen 
of  areolar  tissue  in  the  same  manner  as  the  preceding.  Instead  of  mounting  in 
salt  solution,  allow  it  to  become  perfectly  dry,  then  stain  in  the  following  solution: 

Gentian  violet,  saturated  aqueous  solution,  40  c.c. 

Water,  60  c.c. 

Wash  thoroughly,  dry,  and  mount  in  balsam. 

The  nuclei  of  the  fixed  connective-tissue  cells  are  stained  violet.  Their  deli 
cate  cell  bodies  show  as  an  irregular  haze  around  the  nuclei.  Both  nuclei  and  cell 
bodies  appear  cut  in  all  directions  by  the  stretched  elastic  fibres.  Wandering  cells 
(leucocytes)  may  usually  be  seen.  Plasma  cells  are  frequently  not  demonstrable, 
and  mast  cells  are  only  occasionally  present.  The  elastic  fibres  are  stained  violet. 
The  white  fibres  are  almost  unstained. 

While  these  methods  are  most  satisfactory  for  bringing  out  the  different  connec- 
tive-tissue elements,  they  are  misleading  to  the  student  in  that  they  show  a  picture 
of  connective  tissue  after  special  preparation,  rather  than  as  it  usually  appears  in 
sections.  For  contra.st  the  student  should  study  carefully  the  connective  tissue  as 
it  appears  in  sections  through  the  skin,  the  mucous  membranes  and  other  organs. 

3.  Formed  Connective  Tissue.— Fibrous  tissue  arranged  in  the  form  of  a  net- 
work may  be  seen  in  the  specimen  of  omentum  (technic  7,  p.  72). 

4.  Densely  formed  connective  tissue  may  be  studied  in  tendon.  Cut  through 
the  skin  of  the  tail  of  a  recently  killed  mouse  about  half  an  inch  from  the  tip  and 
break  the  tail  at  this  point.  By  pulling  on  the  end  of  the  tail  this  portion  may  now 
be  separated  from  the  rest  of  the  tail,  carrying  with  it  long  delicate  tendon  fibrils, 
which  have  been  pulled  out  of  their  sheaths.     The.se  should  be  immediately  ex- 


THE  CONNECTIVE  TISSUES.  81 

amined  in  salt  solution,  using  the  high  power  and  a  small  diaphragm.     The  fibrils 
are  seen  arranged  in  parallel  bundles. 

5.  Place  a  drop  of  hydric  acetate  (2-per-cent.  aqueous  solution)  at  one  side  of 
the  cover-glass,  absorbing  the  salt  solution  from  the  opposite  side  bv  means  of 
filter  paper.  The  fibres  swell  and  become  almost  invisible,  while  rows  of  connec- 
tive-tissue cells  (tendon  cells)  can  now  be  seen.  The  cells  may  be  stained  by  allow- 
ing a  drop  of  hsematoxylin  or  of  carmine  solution  to  run  under  the  cover.  After 
the  cells  are  sufficiently  stained,  the  excess  of  stain  is  removed  by  washing,  and  the 
specimen  mounted  in  glycerin. 

6.  Fix  a  small  piece  of  any  good-sized  tendon  in  formalin-Miiller's  fluid  (page 
7.  After  a  week,  harden  in  alcohol,  embed  in  celloidin,  and  make  longitudinal 
and  transverse  sections.  Stain  strongly  with  haematoxylin,  followed  by  picro-acid 
fuchsin  (page  19).     Mount  in  balsam. 

7.  Pigmented  connective-tissue  cells  are  most  conveniently  obtained  from  the 
chorioid  coat  of  the  eye.  Fix  an  eye  in  formalin-Miiller's  fluid  (see  page  7),  cut 
in  half,  remove  chorioid  and  retina  and  pick  off  the  dark  shreds  which  cling  to  the 
outer  surface  of  the  chorioid  and  inner  surface  of  the  sclera.  These  may  be  trans- 
ferred directly  to  glycerin,  in  which  they  are  mounted,  or  the  bits  of  tissue  may  be 
first  stained  with  haematoxylin  (page  15).  In  addition  to  the  pigmented  cells 
should  be  noted  the  ordinary  fixed  connective-tissue  cells  which  lie  among  them. 
Only  the  nuclei  of  these  cells  can  be  seen. 

8.  Connective-tissue  cells  to  show  anastomosing  processes. — Stain  a  cornea 
with  gold  chlorid  (see  page  26).  Sections  are  made  tangential  to  the  convex  sur- 
face and  are  mounted  in  glycerin. 

9.  Connective-tissue  cell  spaces  (lacunse)  and  their  anastomosing  canaliculi 
may  be  demonstrated  by  staining  a  cornea  with  silver  nitrate  (see  page  26).  The 
silver  stains  the  ground  substance  of  the  cornea,  leaving  the  lacuna?  and  canaliculi 
unstained.  The  relation  which  this  picture  bears  to  the  preceding  should  be  borne 
in  mind  (see  Figs.  29  and  30). 

10.  Coarse  elastic  fibres  may  be  obtained  from  the  ligamentum  nuchae,  which 
consists  almost  wholly  of  elastic  tissue.  A  piece  of  the  ligament  is  fixed  in  satu- 
rated aqueous  solution  of  picric  acid  and  hardened  in  alcohol.  A  bit  of  this  tissue 
is  teased  apart  on  a  glass  slide  in  a  drop  of  pure  glycerin,  in  which  it  is  also  mounted. 
Before  putting  into  glycerin,  the  specimen  may  be  stained  with  picro-acid-fuchsin. 
This  intensifies  the  yellow  of  the  elastic  fibers  and  brings  out  in  red  the  fibrillar 
connective  tissue.  Pieces  of  the  ligament  fixed  and  hardened  in  the  same  manner 
may  be  embedded  in  celloidin  and  cut  into  longitudinal  and  transverse  sections. 
These  stained  with  picro-acid-fuchsin  show  well  the  relation  of  the  coarse  elastic 
fibres  (yellow)  to  the  more  delicate  fibrous  tissues  (red). 

3.  Embryonal  and  Mucous  Tissue. 

Embryonal  and  mucous  tissue  are  essentially  de\"elopmental  forms 
and  represent  early  diflferentiations  from  the  general  parent  type. 
They  consist,  according  to  their  age,  of  o\aL  fusiform,  or  irregular 
branching  and  anastomosing  cells,  lying  in  a  matrix,  which  is  just 
beginning  to  show  evidences  of  a  fibrillar  structure.  By  some  his- 
6 


82 


THE  TISSUES. 


tologists  the  term  "embryonic"  connective  tissue  is  limited  to  the 
stage  of  fusiform  cells  with  slightly  fibrillar  matrix  (Fig.  35),  the  term 
"mucous"  tissue  being  applied  to  an  embryonic  form  of  connective 


Fig.  35. — Embryonal  Connective  Tissue  from  Axilla  of  Five-inch  Foetal  Pig.  X6oo. 
(Technic  i,  p.  83.)  Various  shaped  connective-tissue  cells  are  seen  lying  in  a  slightly 
fibrillated  matrix. 


tissue  in  which  irregular  branching  and  anastomosing  cells  lie  in  a 
slightly  fibrillated  matrix  which  gives  the  chemical  reaction  for  mucin 
(Fig.  36). 


Fig.  36.— Mucous  Connective  Tissue  from  Umbilical  Cord  of  Eight-inch  Foetal  Pig. 
X600.     (Technic  2,  p.  83.) 


THE  CONNECTIVE  TISSUES.  83 

Embryonal  tissue  is  not  found  in  the  adult,  while  mucous  tissue 
has  only  a  very  restricted  distribution.  It  constitutes  the  vitreous 
humor  of  the  eye  and  Wharton's  jelly  of  the  umbilical  cord. 

Much  variation  exists  as  to  the  shape  and  size  of  the  cells  in  em- 
bryonal and  mucous  tissue.  This  is  due  to  the  fact  that  these  cells 
represent  transition  stages  in  the  development  of  the  adult  connec- 
tive-tissue cell.  Thus  in  embryonic  connective  tissue,  while  most 
of  the  cells  are  fusiform,  one  finds  spherical  and  oval  cells  and  some 
few  cells  which  are  triangular  or  stellate.  The  same  holds  true  of 
mucous  tissue,  where,  while  most  of  the  cells  are  of  the  triangular 
or  stellate  variety,  round,  oval,  and  fusiform  cells  are  also  present. 

TECHNIC. 

1.  Embryonal  Tissue. — Bits  of  the  subcutaneous  tissue  from  the  axilla  or  groin 
of  a  five-inch  foetal  pig  are  fixed  in  Zenker's  fluid  (technic,  9,  p.  8),  hardened  in 
alcohol  and  stained  for  twelve  hours  in  alum-carmine  (technic  b,  p.  17).  They 
are  then  transferred  to  eosin-glycerin,  in  which  they  are  teased  and  mounted. 
Note  the  intercellular  substance,  that  it  is  composed  of  delicate  single  fibrils  inter- 
lacing in  all  directions  with  no  arrangement  into  bundles,  as  in  adult  tissue,  and 
that  there  is  as  yet  no  differentiation  into  two  kinds  of  fibres. 

2.  Mucous  Tissue. — The  umbilical  cord  of  a  four-  or  five-month  human  foe- 
tus, or  of  a  nine-inch  foetal  pig  is  fixed  in  formalin-Muller's  fluid  (page  7),  hardened 
in  alcohol,  and  transverse  sections  stained  with  haematoxylin-eosin  (technic  i, 
p.  18)  and  mounted  in  eosin-glycerin.  Note  the  central  blood-vessels  with  their 
thick  walls  and  the  surface  epithelium.  The  mucous  tissue  is  best  studied  near  the 
surface  just  beneath  the  epithelium. 

4.  Reticular  Tissue. 

Reticular  connective  tissue  is  a  form  of  fibrillar  connective  tissue. 
It  consists  of  extremely  delicately  fibrillated  connective-tissue  cells 
which  anastomose  to  form  a  reticulum  (Fig.  37).  According  to 
latest  researches  there  are  apparently  no  extracellular  fibres.  Chemic- 
ally it  resembles  white  fibrous  tissue  in  not  being  digested  by  pancreatin. 
It  does  not,  however,  like  ordinary  fibrous  tissue,  yield  gelatin  upon 
boiling  in  water,  but  clastiii  or  a  mixture  of  gelatin  and  elastin,  perhaps 
due  to  the  impossibility  of  wholly  separating  the  two  forms  of  tissue. 
Structurally  white  fibrous  tissue  and  reticular  tissue  are  apparently 
continuous  as  seen  in  the  lymph  node  where  the  larger  masses  of 
fibrous  tissue  which  constitute  the  trabeculas  pass  over  without  demar- 
cation into  the  reticulum  of  the  lymphoid  tissue. 

Reticular  connective  tissue  forms  the  framework  of  adenoid  tissue 


84  THE  TISSUES. 

and  of  bone-marrow.  It  is  also  present  in  large  amounts  in  the  spleen 
and  in  the  mucous  membrane  of  the  gastro-intestinal  tract.  Fibrils 
giving  the  chemical  reaction  of  reticular  tissue  are  associated  with  the 
fibrous  and  elastic-tissue  framework  of  the  lung,  liver,  kidney,  and 


Fig.  37. — Reticular  Connective  Tissue  from  Human  Lymph  Node.      X6oo. 
(Technic,  p.  85.) 

Other  organs.  The  scope  of  the  term  "reticular  tissue"  is  constantly 
broadening,  many  of  the  finer  connective  tissues  formerly  classed  as 
white  fibrous  being  now  considered  reticular. 

5.  Lymphatic  Tissue. 

Lymphatic  tissue  consists  of  reticular  connective  tissue  and  a  spe- 
cial type  of  connective-tissue  cells,  lymphoid  cells,  filling  the  meshes 
of  the  reticulum.  Lymphoid  cells  are  small  spherical  cells.  Each 
cell  has  a  single  nucleus  which  almost  fills  the  cell.  In  lymphatic 
tissue  the  cell  is  a  much  more  important  factor  in  determining  the 
character  of  the  tissue  than  in  most  forms  of  connective  tissue. 

Lymphatic  tissue  may  be  dijfuse  or  circumscribed.  In  diffuse 
lymphatic  tissue  (Fig.  38)  the  cells  are  not  closely  packed  and  there 
is  no  distinct  demarcation  between  the  lymphatic  and  the  surround- 
ing tissues.  An  example  of  diffuse  lymphatic  tissue  is  seen  in  the 
stroma  of  the  mucous  membrane  of  the  gastro-intestinal  canal.  In 
circumscribed  lymphatic  tissue  (Fig.  38)  the  cells  are  very  closely  packed, 
often  completely  obscuring  the  reticulum.  There  is  also  a  quite  distinct 
demarcation  between  the  lymphatic  and  the  surrounding  tissues. 
Such  a  circumscribed  mass  of  lymphatic  tissue  is  known  as  a  lymph 
nodule. 

On  account  of  both  structure  and  function  lymphatic  tissue  might 
more  logically  be  considered  an  organ  than  a  tissue,  for  it  consists  of 


THE  CONNECTIVE  TISSUES. 


85 


a  connective-tissue  framework  supporting  a  special  type  of  cell  which 
has  a  definite  function.  On  account,  however,  of  its  wide  distribu- 
tion and  of  its  close  relations  with  connective  tissue  it  is  most  conveni- 
ently described  here. 


Fig.  38. — Lymphatic  Tissue  from  a  Human  Lymph  Node.  (Technic,  below.)  a, 
Reticular  connective  tissue,  in  the  meshes  of  which  are  suspended  h,  leucocytes,  and  c, 
i\-mphocytes.  The  reticular  connective  tissue  is  present  also  in  the  more  dense  lymphatic 
tissue  seen  in  the  lower  part  of  the  figure,  but  is  not  visible  on  account  of  the  closelv  packed 
cells. 

TECHNIC. 

Fi.x  a  lymph  node  in  formalin-Muller's  fluid  (technic  5,  p.  7),  and  stain  very 
thin  sections  with  haematoxylin  and  picro-acid  fuchsin  (technic  3,  p.  19).  In  the 
lymph  sinuses  of  the  medulla  the  reticulum  can  usually  be  plainly  .seen. 

6.  Fat  Tissue. 

Adipose  tissue  or  fat  tissue  is  a  form  of  connective  tissue  in  which 
some  of  the  cells  have  become  changed  into  fat  cells.  Fat  tissue  is 
peculiar  among  the  connective  tissues  in  that  the  cells  and  not  the 
intercellular  substance   make   up   the   bulk  and   determine   the  char- 


86 


THE  TISSUES. 


acter  of  the  tissue.  The  adult  fat  cell  is  surrounded  by  a  distinct 
cell  membrane,  and  almost  the  entire  cell  is  occupied  by  a  single  spheri- 
cal droplet  of  fat  (Figs.  40  and  41).  The  nucleus,  flattened  and  sur- 
rounded by  a  small  amount  of  cytoplasm,  is  usually  found  pressed 
against  the  cell  wall  (Fig.  41).  This  appearance  of  a  distinct  cell 
membrane  enclosing  the  spherical  fat  droplet,  with  the  nucleus  and 
cytoplasm  pressed  into  a  crescent-shaped  mass  at  one  side,  has  given 
rise  to  the  term  "signet-ring  cell."  Fat  cells  which  occur  singly,  or  in 
small  groups,  or  in  the  developing  fat  of  young  animals,  are  spherical 


Fig.  39. — Fat  Tissue  from  Human  Subcutaneous  Tissue  (Child)  to  show  Lobulation. 
X25.      (Technic  i,  p.  8q.) 

(Fig.  40).  In  large  masses  of  adult  fat,  the  closely  packed  cells  are 
subjected  to  pressure  and  are  polyhedral  (Fig.  41).  Fat  cells  are 
usually  arranged  in  groups  or  lobules,  each  lobule  being  separated  from 
its  neighbors  by  fibrillar  connective  tissue  (Fig.  39).  Adipose  tissue  is 
usually  associated  with  loose  fibrous  tissue. 

The  appearance  which  adult  fat  presents  can  be  understood  only 
by  reference  to  its  histogenesis.  Fat  cells  are  developed  directly 
from  embryonic  connective-tissue  cells.  In  the  human  embryo  they 
arc  first  distinguishable  as  fat  cells  about  the  thirteenth  week.  The 
connective-tissue  cells  which  are  to  become  fat  cells  gather  in  groups  in 
the  meshes  of  the  capillary  network  which  marks  the  ending  of  a  small 
artery.     Each  group  is  destined  to  become  an  adult  fat  lobule  (Fig.  42) 


THE  CONNECTIVE  TISSUES. 
b 


87 


Fig.  40. — Young  Fat  from  Human  Subcutaneous  Tissue  (Child).  X175.  (Technic 
I,  p.  89.)  a,  InterlolDular  connective  tissue;  b,  fixed  connective-tissue  cell;  c,  fat  cells;  d, 
artery;  e,  nucleus  of  fat  cell  and  remains  of  cytoplasm  ("signet  ring"). 


d 
Fig.   41. — Adult  Fat  Tissue  from  Human  Subcutaneous  Tissue.      X175.      (Technic 
p.  8g.)     a.  Fat  cells;  b,  interlobular  conncctixe  tissue;  c,  nucleus  of  fat  cell  and  remain* 
cytoplasm  ("signet  ring");  </,  ariery. 


88 


THE  TISSUES. 


Fat  first  appears  as  minute  droplets  in  the  cytoplasm  of  the  em- 
bryonic  connective-tissue   cell    (Fig.   43).     These   small   droplets   in- 


FiG.  42. — Developing  Fat  Tissue  from  Subcutaneous  Tissue  of  Five-inch  Foetal  Pig. 
X75.  (Technic  2,  p.  8q.)  a,  Arteriole  breaking  up  into  capillary  network;  h,  embryonal 
connective  tissue;  c,  embryonal  fat  lobules  developing  around  blood-vessels. 


[0^ 


m 


Fig.  43. — Developing  I'at  Tissue  fnjm  Subcutaneous  Tissue  of  Five-inch  Foetal  Pig. 
(Technic  2,  pj.  89.)  «,  Arteriole  breaking  up  into  capillary  network;  b,  embryonal  connec- 
tive tissue,  embryonal  cells  fr(mi  which  fat  cells  are  developing;  c,  capillaries.  Fat  droplets 
stainerl  black.  At  the  right  are  five  individual  lells  showing  stages  of  development  frf)m 
an  embryonal  cell  to  an  adult  fat  cell. 

crease  in  number  and  finally  coalesce  to  form  a  single  larger  droplet. 
'Fhis  increases  in  size  and  ultimately  almost  wholly  replaces  the  cyto- 


THE  CONNECTR-E  TISSUES.  89 

plasm.  In  this  way  the  nucleus  and  remaining  cytoplasm  are  pressed 
to  one  side  and  come  to  occupy  the  inconspicuous  position  which  they 
have  in  adult  fat. 

The  blood  supply  of  fat  is  rich  and  the  adult  lobule  maintains  its 
embryonic  vascular  relations,  in  that  the  vascular  supply  of  each  lobule 
is  complete  and  independent.  One  artery  runs  to  each  lobule,  where 
it  breaks  up  into  an  intralobular  capillary  network,  which  in  turn  gives 
rise  to  the  intralobular  veins,  usually  two  in  number. 

Fat  is  thus  seen  to  be  a  connective  tissue  in  which  some  of  the  cells 
have  undergone  specialization.  There  still  remain,  however,  embryonal 
connective-tissue  cells  which  are  not  destined  to  become  fat  cells,  but 
which  develop  into  cells  and  fibres  of  ordinary  fibrous  connective 
tissue.  A  few  of  these  remain  among  the  fat  cells  to  become  the  delicate 
intralobular  connective  tissue  seen  in  adult  fat.  The  majority  are, 
however,  pushed  to  one  side  by  the  developing  lobules,  where  they 
form  the  interlobular  septa. 

TECHNIC. 

1.  Fat  Tissue. — Human  subcutaneous  fat  as  fresh  as  possible  is  fixed  in  forma- 
lin-Miiller's  fluid  (technic  5,  p.  7),  hardened  in  alcohol  and  embedded  in  celloidin. 
Sections  are  stained  with  haematoxyUn  and  picro-acid-fuchsin  (technic  3,  p.  19). 
The  alcohol  and  ether  of  the  celloidin  remove  the  fat  from  the  fat  cells,  leaving 
only  the  cell  membranes.  The  fat  gives  the  celloidin  a  milky  appearance.  Such 
celloidin  does  not  cut  well.  The  celloidin  should,  therefore,  be  changed  until  it 
ceases  to  turn  white.  The  sections  are  cleared  in  oil  of  origanum  or  carbol-.xylol, 
and  mounted  in  balsam.  The  fibrillar  tissue  is  stained  red  by  the  fuchsin,  and  the 
protoplasm  of  the  fat  cell  yellow  by  the  picric  acid. 

2.  Developing  Fat  Tissue. — Remove  bits  of  tissue  from  the  axilla  or  groin  of 
a  five-inch  foetal  pig,  or  other  fcetus  of  about  the  same  development.  Fix  twenty- 
four  hours  in  a  i-per-cent.  aqueous  solution  of  osmic  acid  (technic  8,  p.  28),  wash 
thoroughly  and  mount  in  glycerin.  A  part  of  the  tissue  mounted  should  be  thor- 
oughly teased,  the  rest  gently  pulled  apart.  The  teased  portion  will  show  the  fat 
cells  in  various  stages  of  development.  The  unteased  part  will  usually  show  brown- 
ish blood-vessels  and  the  grouping  of  fat  cells  around  them,  to  form  embryonic 
fat  lobules.  Note  the  developing  connective  tissue  between  the  groups  of  fat 
cells.  It  is  from  this  that  the  areolar  tissue,  which  envelops  and  separates  the 
lobules  of  adult  fat,  is   developed. 

7.  Cartilage. 

Cartilage  is  a  form  of  connective  tissue  in  which  the  ground  sub- 
stance is  firm  and  dense  and  determines  the  physical  character  of  the 
tissue.     (3n   boilinti;   it   vields   chondriu.     Cartila^jc  cells   are   differen- 


90 


THE  TISSUES. 


tiated  connective-tissue  cells.  While  varying  greatly  in  shape  they  are 
most  frequently  spherical  or  oval.  Each  cell  Hes  in  a  cell  space  or 
lacuna,  which  it  completely  fills.  The  intercellular  substance  immedi- 
ately surrounding  a  lacuna  is  frequently  arranged  concentrically,  form- 
ing a  sort  of  capsule.  Fine  canaliculi  connecting  the  lacunae  are  present 
in  some  of  the  lower  animals  and  have  been  described  in  human  carti- 
lage. They  can  be  demonstrated,  however,  in  human  cartilage,  only  by 
special  methods,  and  probably  represent  artefacts. 

Cartilage   contains  no  blood-vessels,  and  in  human  cartilage  no 
lymph  channels  have  been  positively  demonstrated. 


■  -?;    ^  .-:>■  -''' 

(S^ 

'S::^ 

^     'it  )) 

!/'fi 

vVv 

/«--. 
^"^^v- 

:    -A- 

3^ 

f'S 

mm 

-lis 

Fig.  44. — Hyaline  Cartilage  from  Head  of  Frog's  Femur.      X350.     (Technic  i,  p.  c,2.) 
Groups  of  cartilage  cells  in  apparently  homogeneous  matrix. 

Cartilage  is  subdivided  according  to  the  character  of  its  intercel- 
lular substance  into  three  varieties:  (i)  Hyaline,  (2)  elastic,  (3)  fibrous. 

I.  Hyaline  Cartilage  (Fig.  44). — The  cells  occur  singly  or  in 
groups  of  two  or  multiples  of  two.  An  entire  group  of  cells  frequently 
lies  in  one  lucuna  surrounded  by  a  single  capsule.  Such  a  group  of 
cells  has  developed  within  its  capsule  from  a  single  parent  cell.  In 
other  cases  delicate  hyaline  partitions  separate  the  cells  of  a  group. 
The  cells  are  spherical  or  oval,  with  flattening  of  adjacent  sides.  The 
nucleus  is  centrally  placed,  and  has  a  distinct  intranuclear  network  and 
membrane.  The  cytoplasm  is  finely  granular,  and  may  contain  drop- 
lets of  fat,  of  glycogen,  or  of  both.  Toward  the  perichondrium  the 
arrangement  of  the  cells  in  groups  is  less  distinct.  Here  the  cells  are 
fusiform  and  parallel  to  the  surface. 


THE  CONNECTR'E  TISSUES. 


91 


The  intercellular  matrix,  when  subjected  to  the  usual  technic, 
appears  homogeneous.  By  the  use  of  special  methods,  such,  e.g.,  as 
artificial  digestion,  this  apparently  structureless  matrix  has  been  shown 
to    be    made    up    of  bundles  of 


■^ 


^^'\iy>r^ 


-^wr^^i 


^ 


da^ 


>>^' 


fibres,  quite  similar  to  those 
found  in  fibrous  connective 
tissue. 

Hyaline  cartilage  forms  the 
articular  cartilages  of  joints,  the 
costal  cartilages,  and  the  carti- 
lages of  the  nose,  trachea,  and 
bronchi.  In  the  embryo  a  young 
type  of  hyaline  cartilage,  known 
as  embryonal  cartilage,  forms  the 
matrix  in  which  most  of  the 
bones  are  developed. 

2.  Elastic  cartilage  (Fig.  45) 
resembles  hyaline,  but  differs 
from  the  latter  in  that  its  hyaline  matrix  contains  a  large  number  of 
elastic  fibres.  These  vary  in  size,  many  being  extremely  fine.  The 
elastic  fibres  branch  and  run  in  all  directions,  forming  a  dense  net- 
work of  interlacing  and  anastomosing  fibres. 


W^^' 


'^.u 


Fig.  45. — Elastic  Cartilage  from  Dog's  Ear. 
X350.  (Technic  2,  p.  Q2.)  Groups  of 
cartilage  cells  in  fibre-elastic  matrix. 


=-~     >^^ 


l^iQ    46.— Fibrous  Cartilage  from  Dog's  Intervertebral  Disc.      X350.     (Technic  3,  p.  92.) 
Groups  of  cartilage  cells  in  matrix  of  fibrillar  connective  tissue. 

Elastic  cartilage  occurs  in  the  external  ear,  the  Eustachian  tube, 
the  epiglottis,  and  in  some  of  the  laryngeal  cartilages. 

3.  Fibrous   cartilage    (Fig.   46)   is  composed   mainly  of    fibrillar 


92  THE  TISSUES. 

connective  tissue.  The  fibres  may  have  a  parallel  arrangement,  or 
may  run  in  all  directions.  Cells  are  few,  and  are  usually  arranged 
in  rows  of  from  two  to  six,  lying  in  elongated  cell  spaces  between  the 
fibre  bundles. 

Fibrous  cartilage  occurs  in  the  inferior  maxillary  and  sterno- 
cla^"icular  articulations,  in  the  symphysis  pubis,  and  in  the  interver- 
tebral discs. 

Cartilage,  except  where  it  forms  articular  surfaces,  is  covered  by 
a  membrane,  the  perichondrium.  This  is  composed  of  fibrillar  con- 
nective tissue,  and  blends  without  distinct  demarcation  with  the  super- 
ficial layers  of  the  cartilage. 

Like  the  other  connective  tissues,  cartilage  develops  from  mesoderm. 
It  is  at  first  wholly  cellular.  Each  cell  forms  a  capsule  around 
itself,  and  by  blending  of  these  capsules  are  formed  the  first  elements  of 
the  intercellular  matrix.  This  increases  in  quantity  and  assumes  the 
structural  characteristics  of  one  of  the  forms  of  cartilage.  The  white 
fibres  of  fibro-cartilage  and  the  yellow  fibres  of  elastic  cartilage  develop 
in  the  same  manner  as  in  fibrillar  and  elastic  tissue. 

TECHNIC. 

(i)  Hyaline  Cartilage. — Remove  a  frog's  femur  and  immediately  immerse  the 
head  in  saturated  aqueous  solution  of  picric  acid.  Cut  sections  tangential  to  the 
rounded  head,  keeping  knife  and  bone  wet  with  the  picric  acid  solution.  As  bone 
must  be  cut,  a  special  razor  kept  for  the  purpose  should  be  used.  Cut  sections  as 
thin  as  possible.  The  first  sections  consist  wholly  of  cartilage.  As  bone  is  reached, 
the  cartilage  is  confined  to  a  ring  around  the  bone.  Mount  in  the  picric-acid  solu- 
tion, cementing  the  cover-glass  immediately. 

{2)  Elastic  Cartilage. — Remove  a  piece  of  cartilage  from  the  ear  and  fix  in 
formalin-Miiller's  fluid  (technic  5,  p.  7).  Stain  sections  strongly  with  hasmatoxylin, 
followed  by  picro-acid-fuchsin  (technic  3,  p.  19).  Clear  in  carbol-xylol  and  mount 
in  balsam.  The  capsules  around  the  cartilage  cells  are  thick  and,  as  they  usually 
retain  some  hsematoxylin,  can  be  readily  seen.  Note  also  the  flattened  cartilage 
cells  near  the  surface,  and  the  perichondrium. 

(3)  Fibro-cartilage. — Fix  pieces  of  an  intervertebral  disc  in  formalin-Miiller's 
fluid.  Sections  are  stained  either  with  haematoxylin-eosin  or  with  haematoxylin- 
picro-acid-fuchsin  and  mounted  in  balsam. 

8.  Bone  Tissue. 

Bone  is  a  form  of  connective  tissue  in  which  the  matrix  is  ren- 
dered hard  by  the  deposition  in  it  of  inorganic  matter,  chiefly  the 
phosphate  and  the  carbonate  of  calcium.     These  salts  are  not  merely 


THE  COXXECTRE  TISSUES. 


93 


Fig.  47. — Bone  Tissue  showing  Lacunae  and 
Canaliculi.      X700.     (Technic  i,  p.  94.) 


deposited  in  the  matrix,  but  are  intimately  associated  and  combined 
with  its  histological  structure.  The  intimacy  of  this  association  of 
the  organic  and  inorganic  constituents  of  bone  is  shown  by  the  fact 
that,  though  the  salts  compose  two-thirds  of  bone  by  weight,  it  is 
impossible  to  distinguish 
them  by  the  highest  magnifi- 
cation.  Furthermore,  if 
either  the  lime  salts  are  dis- 
solved out  by  means  of  acids 
(decalcification)  or  the  or- 
ganic matter  removed  by 
heating  (calcination),  the 
histological  structure  of  the 
bone  still  remains. 

Like  the  other  connec- 
tive tissues,  bone  consists 
morphologically  of  cells  and 
intercellular  substance. 

Bone  cells  or  hone  corpuscles  lie  in  distinct  cell  spaces  or  lacunce. 
From  the  lacuna  pass  off  in  all  directions  minute  canals — canaliculi — 
which  anastomose  with  canaliculi  of  neighboring  lacunae  (Fig.  47). 
At  the  surface  of  bone  these  canaliculi  open  into  the  periosteal  lymph- 
atics. A  complete  system  of  canals  is  thus  formed,  which  traverse 
the  bone  and  serve  for  the  passage  of  nutri- 
tive fluids.  The  bone  cells  themselves  (Fig. 
48)  are  flat,  ovoid,  nucleated  cells,  with 
numerous  fine  processes,  wdiich  extend  in  all 
directions  into  the  canaliculi.  In  young  de- 
veloping bones  the  processes  of  adjacent  cells 
anastomose.  In  adult  bone  the  processes  ex- 
tend but  a  short  distance  into  the  canaliculi. 
and  probably  do  not  anastomose. 

The  basement  substance  or  matrix  has  a 
fibrous  structure,  closely  resembling  that  of 
fibrillar  connective  tissue,  and  it  is  in  this 
fibrillar  matrix  that  the  lime  salts  are  deposited.  The  fibrils  are  held 
together  by  cement  substance  into  bundles.  In  most  bone  the  bundles 
are  fine  and  arranged  in  layers  or  lamcllcr.  Less  commonly  the  fibre 
bundles  are  coarser  and  ha^"C  an  irregular  arrangement. 


Fig.  48. — Bone  Cell  and 
Lacuna.  (After  Joseph.) 
At  a  the  cell  body  has 
shrunken,  allowing  the 
outline  of  the  lacuna  to  be 
seen. 


94  THE  TISSUES. 

TECHNIC. 

(i)  For  the  study  of  the  minute  structure  of  bone  a  section  of  undecalcified  or 
hard  bone  is  required.  Part  of  the  shaft  of  one  of  the  long  bones  is  soaked  for  sev- 
eral days  in  water  and  all  the  soft  parts  are  removed.  It  is  then  placed  in  equal 
parts  alcohol  and  ether  to  remove  all  traces  of  fat  and  thoroughly  dried  (the  handle 
of  a  tooth  or  nail  brush  frequently  furnishes  good  material  and  is  already  dried). 
Thin  longitudinal  and  transverse  sections  are  now  cut  out  with  a  bone  saw.  One 
surface  is  next  ground  smooth,  first  on  a  glass  plate,  using  emery  and  water,  then 
on  a  hone.  The  specimen  is  now  fastened  polished  side  down  on  a  block  of  wood 
or  glass  by  means  of  sealing  wax,  and  the  other  side  polished  smooth  in  the  same 
manner  as  the  first,  the  bone  being  ground  as  thin  as  possible.  The  sealing  wax  is 
removed  by  soaking  in  alcohol  and  the  specimen  looked  at  with  the  low  power. 
If  not  thin  enough,  it  is  gently  rubbed  on  a  fine  hone.  It  is  then  soaked  in  equal 
parts  alcohol  and  ether,  dried  thoroughly,  and  mounted  in  hard  balsam.  This  is 
accomplished  by  placing  a  small  bit  of  hard  balsam  on  a  slide,  melting,  pushing  a 
bit  of  the  bone  into  the  hot  balsam,  covering  and  cooling  as  quickly  as  possible. 
The  object  of  the  hard  balsam  and  quick  cooling  is  to  prevent  the  balsam  running 
into  the  lacunae  and  canaliculi  and  obscuring  them  by  its  transparency.  The  air 
imprisoned  in  the  lacunae  and  canaliculi  causes  them  to  appear  black  when  viewed 
by  reflected  light. 

(2)  The  structure  of  the  bone  cell  is  best  studied  in  sections  of  decalcified  bone 
which  has  first  been  carefully  fixed.     (See  technic  i,  p.  171.) 

9.  Neuroglia. 

This  peculiar  form  of  connective  tissue  is  confined  entirely  to  the 
central  nervous  system  and  is  most  conveniently  studied  in  connec- 
tion with  nervous  tissue  (see  page  125). 


CHAPTER  IV. 
THE  BLOOD. 

Blood  is  best  considered  as  a  tissue,  the  intercellular  substance 
of  which  is  fluid.  This  fluidity  of  the  intercellular  substance  allows 
the  formed  elements  or  cells  to  move  about  freely,  so  that  there  is  not  the 
same  definite  and  fixed  relation  between  cells  and  intercellular  sub- 
stance as  in  other  tissues. 

The  fluid  intercellular  substance  or  plasma  is  slightly  alkaline  in 
reaction.  It  consists  of  serum  albumen,  globulin,  fibrinogen  and 
inorganic  salts,  chiefly  the  chlorid,  carbonate, 

and  bicarbonate  of  soda.     Its  specific  gravity     '   .  ff •«*««« 

is  about  i.o^o,  while  that  of  the  whole  blood  ♦  ♦    i*«*«»«« 

IS  about   1.060.     The  bulk  of  the  plasma  is  ' 

about  equal  to  that  of  the  red  and  the  white      ^     gj^     g^       ^^^ 
cells.  ,        "      ^P      ^P 

The  formed  elements  of  the  blood  are: 


(i)    Red  blood  cells   (red  blood  corpuscles,      '.'{.it*:      iSSi?; 
erythrocytes);  (2)  white  blood  cells  (colorless      '■  ;•  •*f%v...- 

corpuscles— leucocytes) ;     (3)    blood    platelets    Fig.    49.— Cells   from    Human 

(thrombocytes);     (4)     blood     dust     (hama-      Blood     x6oo^    (Technic  2 

.    ,  P-  100.)       I,    Red    blood  cell 

tokonia).  seen  on  flat;  2,  red  blood  cell 

I.  Red  blood  cells  (erythrocytes)    (Fig.      rdis  S,™lf  iotie^'x:*"' 

49,  1,2,3)  are  in  man  non-nucleated  circular  small  and  large  lymphocytes; 
J.         1        rni     •  T  •         1  ^'  niononuclear  leucocyte;  6, 

discs.        iheir   average    diameter   is   about      transitional     leucocyte;     7, 

7.5,«,  their  thickness  2n  at  the  thin  centre.  Polymorphonuclear  leuco- 
'     ""  '  _  '  cyte,  containing    neutrophile 

They  are    biconcave,   with    rounded    edges.      granules;  8,  polynuclear  leu- 

o  ,1       n    ,     ,1        ^•rc  •        1  •   1  cocyte,     containing     eosino- 

been  on  the  flat,  the  dinerence  in  thickness  phiie  granules;  q,  mononu- 
between  centre   and  periphery  is  evidenced      r'^'^*"  ,  leucocyte    containing 

^        ^         "^  basophile  granules. 

by  the  difference  in  refraction  (Fig.  49,  i). 

Seen  on  edge,  the  shape  resembles  that  of  a  dumb-bell  (Fig.  49,  2). 
Singly  or  in  small  numbers,  red  blood  cells  have  a  pale  straw  color. 
Redness  of  the  cells  is  apparent  only  when  they  are  seen  in  large 
numbers.     If  fresh  blood  be  allowed  to  stand  for  a  moment,  the  red 

'Some  observers  describe  the  red  blood  ceil   as  bell- or  cup-shaped.      (Lewis:    Jour. 
INIed.  Research,  X.  S.,  vol.  v,  IQ04.) 

9.) 


96  THE  TISSUES. 

cells  are  seen  to  adhere  to  one  another  by  their  flat  surfaces,  forming 
rows  or  rouleaux  (Fig.  49,  3). 

Subjected  to  the  usual  technic,  the  red  blood  cell  appears  homo- 
geneous. By  the  use  of  special  methods,  this  apparently  homogeneous 
substance  can  be  separated  into  (a)  a  color-bearing  proteid — hcemo- 
globin,  and  (b)  a  stroma,  the  latter  representing  the  protoplasm  of  the 
cell.  It  is  the  haemoglobin  which  gives  color  to  the  corpuscles.  Haemo- 
globin is  a  complex  proteid,  and  is  held  in  solution  or  in  suspension 
in  the  stroma,  which  can  be  resolved  into  a  globulin  and  a  pigment, 
hamatin. 

The  red  blood  cells  are  soft  and  elastic,  and  are  easily  twisted 
to  accommodate  themselves  to  the  smallest  capillaries. 

The  red  blood  cell  is  extremely  susceptible  to  changes  in  the  plasma. 
Thus  even  slight  evaporation  of  the  plasma  results  in  osmosis  between 
the  now  denser  surrounding  fluid  and  the  contents  of  the  cell.  This 
causes  fluid  to  leave  the  cell,  with  the  result  that  the  latter  becomes 
spheroidal  and  irregularly  shrunken,  with  minute  knob-like  projec- 
tions from  its  surface.  This  is  known  as  crenation  of  the  red  cell. 
The  addition  of  water  to  blood,  thus  decreasing  the  specific  gravity 
of  the  plasma,  has  the  opposite  effect,  resulting  in  swelling  of  the  cell. 
It  also  causes  solution  of  the  haemoglobin,  which  leaves  the  cell,  the 
latter  then  appearing  colorless.  This  separation  of  the  haemoglobin 
from  the  corpuscle  is  also  caused  by  freezing  and  thawing,  by  heat 
(60°  C),  by  the  addition  of  dilute  acids,  ether,  or  chloroform. 

Dilute  alkaline  solutions  and  bile  first  cause  the  red  corpuscles  to 
swell  and  become  spherical,  and  then  to  dissolve.  This  is  known 
as  haemolysis,  and  may  also  be  effected  by  mixing  the  blood  of  one 
species  with  that  of  another.  Dilute  acetic  acid  causes  swelling  and 
fading  of  the  red  cells,  with  the  formation  of  prismatic  crystals  of 
haemoglobin. 

The  red  blood  cells  number  from  4,500,000  to  5,000,000  per  cubic 
millimetre  of  blood. 

2.  White  blood  cells  (leucocytes)  (Fig.  49,  4  to  9  inclusive)  are 
colorless  nucleated  structures  which  have  a  generally  spherical  shape, 
but  which  are  able  to  change  their  shape  on  account  of  their  powers 
of  amoeboid  movement.  They  have  a  diameter  of  from  5  to  io/<, 
and  are  much  less  numerous  than  the  red  cells,  the  proportion  being 
about  one  white  cell  to  from  three  hundred  to  six  hundred  red  cells. 
This  proportion  is,  however,  subject  to  wide  variation. 

Leucocytes  may  be  classified  as  follows:   (a)    Lymphocytes;    {b) 


THE  BLOOU.  97 

mononuclear    leucocytes;    (c)    transitional    leucocytes;    (d)    polymor- 
phonuclear or  polynuclear  leucocytes. 

{a)  Lymphocytes  (Fig.  49,  4). — These  vary  in  diameter  from  5 
to  8/i,  and  are  sometimes  subdivided  into  small  lymphocytes  and  large 
lymphocytes.  The  nucleus  is  spherical,  stains  deeply,  and  almost 
completely  fills  the  cell,  the  cytoplasm  being  confined  to  a  narrow  zone 
around  the  nucleus.  Lymphocytes  constitute  about  20-per-cent.  of 
the  white  blood  cells. 

(b)  Mononuclear  leucocytes  (Fig.  49,  5  and  9)  are  of  about 
the  same  size  as  large  lymphocytes.  The  nucleus,  however,  stains 
more  faintly  and  is  smaller,  while  the  cytoplasm  is  greater  in  amount. 
From  2-per-cent.  to  4-per-cent.  of  the  white  cells  are  mononuclear 
leucocytes. 

{c)  Transitional  leucocytes  (Fig.  49,  6)  occur  in  about  the 
same  numbers  as  the  preceding,  and  are  of  about  the  same  size.  There 
is  relatively  more  cytoplasm,  and  the  nucleus,  instead  of  being  spherical, 
is  crescentic  or  horseshoe  or  irregular  in  shape.  These  cells  represent 
a  traditional  stage  between  the  mononuclear  and  the  polymorpho- 
nuclear and  polynuclear  varieties. 

{d)  Polymorphonuclear  and  polynuclear  leucocytes  (Fig. 
49,  7,  8)  constitute  about  70-per-cent.  of  the  white  blood  cells.  Their 
size  is  about  the  same  as  that  of  the  mononuclear  form,  but  they  are 
somewhat  more  irregular  in  shape.  The  appearance  of  the  nucleus 
is  characteristic.  In  the  polymorphonuclear  form  the  nucleus  con- 
sists of  several  round,  oval,  or  irregular  nuclear  masses  connected 
with  one  another  by  cords  of  nuclear  substance.  These  cords  are 
frequently  so  delicate  as  to  be  distinguished  with  diflficulty.  The 
polynuclear  form  is  derived  from  the  polymorphonuclear  by  breaking 
down  of  the  connecting  cords,  leaving  several  separate  nuclei  or 
nuclear  segments. 

The  protoplasm  of  about  70-per-cent.  of  leucocytes  is  granular,  and 
these  granules  present  very  definite  reactions  when  subjected  to  certain 
aniline  dyes. 

Aniline  dyes  may  be  divided  into  acid,  basic,  and  neutral,  accord- 
ing to  whether  the  coloring  matter  is  an  acid,  a  base,  or  a  combina- 
tion of  an  acid  and  a  base. 

Upon  the  basis  of  their  reaction  to  these  dyes,  Ehrlich  divides 
these  granules  into  five  groups,  which  he  designates  by  the  first  five 
letters  of  the  Greek  alphabet. 

a-Granules   {acidophile,  or,  because  the  most  common  acid  dye 
7 


98  THE  TISSUES. 

used  is  eosin,  eosinophile — Fig.  49,  8).  These  are  coarse,  sharply 
defined  granules  which  stain  intensely  with  acid  dyes.  Eosinophile 
cells  are  mainly  of  the  polynuclear  and  polymorphonuclear  types. 
More  rarely  transitional  forms  contain  eosinophile  granules.  They 
are  actively  amoeboid.  Eosinophile  cells  constitute  from  i-per-cent. 
to  4-per-cent.  of  the  leucocytes  of  normal  blood.  Under  certain 
pathological  conditions  the  number  of  eosinophile  leucocytes  is  greatly 
increased. 

/^-Granules  {amphophile) .  These  are  very  fine  granules,  which 
react  to  both  acid  and  basic  dyes.  /?- Granules  are  not  found  in  nor- 
mal human  blood.  They  are  found  in  the  blood  cells  of  some  of  the 
lower  animals. 

^-Granules  (basophile)  are  small  granules  which  stain  with  basic 
dyes.  They  occur  in  the  so-called  Mastzellen  (p.  75),  which  are  of 
rare  occurrence  in  normal  blood.  They  are  present  in  certain 
pathological  conditions,  and  are  found  normally  in  the  blood  cells 
of  some  of  the  lower  animals,  and  in  some  of  the  cells  of  connective 
tissue. 

8-Granules  (basophile)  are  small  granules,  which  stain  with  basic 
dyes  (Fig.  49,  9).  They  are  found  mainly  in  the  mononuclear  leuco- 
cytes. 

c- Granules  (neutrophile)  react  to  mixtures  of  acid  and  basic  dyes. 
£- Granules  are  the  most  common  of  all  granules,  occurring  in  most  of 
the  polynuclear  and  polymorphonuclear  forms,  being  thus  present  in 
about  68-per-cent.  of  all  white  blood  cells  (Fig.  49,  7). 

Through  their  powers  of  amoeboid  movement  leucocytes  are  able 
not  only  to  pass  through  the  walls  of  the  vessels — diapedesis — and 
out  into  the  tissues,  but  to  wander  about  more  or  less  freely  in  the 
tissues.  Both  inside  and  outside  of  the  vessels  the  leucocytes  have 
an  important  function  to  perform  in  the  taking  up  and  disposal  of 
waste  or  superfluous  materials  and  foreign  particles.  This  is  known 
as  phagocytosis,  and  the  cells  thus  engaged  are  known  as  phagocytes. 
Phagocytosis  plays  an  extremely  important  role  both  in  normal  and  in 
certain  pathological  processes. 

3.  The  blood  platelets  (thrombocytes)  are  minute  round  or  oval 
bodies  about  2//  in  diameter.  They  are  clear  (colorless),  and  are 
described  by  some  as  containing  chromatin  granules,  by  others  as 
having  distinct  nuclear  structures.  They  may  be  separated  by  the 
action  of  a  lo-per-cent.  saline  solution  into  two  elements — one  hya- 
line, the  other  granular.     They  are  said  to  possess  amoeboid  properties 


THE  BLOOD.  99 

and  to  be  concerned  in  the  coagulation  of  the  blood.  They  number 
about  200,000  per  cubic  millimetre. 

4.  The  blood  dust  (hasmatokonia)  occurs  in  the  form  of  small 
refractive  granules. 

In  the  blood  of  the  lower  mammals  and  in  herbivorous  animals 
small  droplets  of  fat  derived  from  the  chyle  are  found.  They  are 
known  as  elementary  granules  and  are  not  present  in  normal  human 
blood. 

Development  of  the  Blood. 

At  an  early  stage  of  embryonic  development  certain  mesodermic 
cells  of  the  area  vasculosa,  which  surrounds  the  embryo,  become 
arranged  in  groups  known  as  hlood  islands.  It  is  from  these  "islands" 
that  both  blood  and  blood-vessels  develop.  The  peripheral  cells 
arrange  themselves  as  the  primitive  vascular  wall,  within  which  the 
central  cells  soon  become  free  as  the  first  hlood  corpuscles.  In  this 
way  vascular  channels  are  formed,  inside  of  which  are  developing  blood 
cells.  These  channels,  which  are  at  first  unconnected,  anastomose 
and  give  rise  to  a  network  of  channels  which  are  the  earliest  capil- 
laries. As  regards  the  origin  of  the  later  vessels  both  within  the 
embryo  and  in  the  extraembryonic  area,  two  views  are  held;  (i)  that 
they  are  outgrowths  from  the  earliest  capillaries;  (2)  that  they  arise 
in  situ  in  the  same  manner  as  the  earliest  capillaries  and  unite 
secondarily  to  form  networks.  The  weight  of  evidence  at  present 
favors  the  latter  view.  These  networks  of  capillaries  at  first  consti- 
tute the  entire  vascular  system.  As  development  proceeds  some  of 
the  channels  enlarge  to  form  the  arteries  and  veins,  the  smooth 
muscle  and  connective  tissue  of  their  walls  dift'erentiating  from  the 
surrounding  mesoderm.  At  first  the  formed  elements  of  blood 
consist  almost  wholly  of  nucleated  red  cells.  These  undergo  mitotic 
division  and  multiply  within  the  vessels.  Two  views  are  held  in  regard 
to  the  manner  in  which  the  embryonic  nucleated  red  cell  gets  rid  of  its 
nucleus  in  becoming  the  non-nucleated  red  cell  of  the  adult.  Accord- 
ing to  one  the  nucleus  is  absorbed  within  the  cell;  according  to  the  other 
the  nucleus,  as  a  whole,  is  extruded. 

In  early  embryonic  life  especially  active  proliferation  of  red  cells 
occurs  in  the  blood-vessels  of  the  liver.  This  has  led  to  the  consider- 
ing of  the  liver  as  a  blood-forming  organ.  The  liver  cells  themselves, 
however,  taken  no  actual  part  in  the  formation  of  blood  cells,  the  blind 
pouch-like  venous  capillaries  of  tlic  li\"er,  willi  their  slow-mo\ing  l:)lood 


100  THE  TISSUES. 

currents,  merely  furnishing  a  peculiarly  suitable  place  for  cellular  pro- 
liferation. Before  birth  the  splenic  pulp  and  bone  marrow  become 
blood-forming  organs.  In  the  adult  the  bone  marrow  is  probably, 
under  normal  conditions,  the  main  if  not  the  sole  seat  of  red-cell 
formation. 

During  fcetal  life  the  number  of  nucleated  red  cells  constantly 
diminishes  while  the  number  of  non-nucleated  red  cells  increases. 
At  birth  there  are  usually  but  few  nucleated  red  cells  in  the  general 
circulation,  although  even  in  the  adult  they  are  always  found  in  the 
red  bone-marrow. 

The  earliest  embryonic  blood  contains  no  white  cells. 

The  origin  of  the  leucocytes  is  not  well  understood.  It  seems 
probable  that  the  earliest  leucocytes  are  derived  like  the  red  cells 
from  the  cells  of  the  blood  islands  of  the  area  vasculosa.  Later  they 
are  formed  in  widely  distributed  groups  of  cells,  lymph  nodules, 
which  are  found  in  various  tissues  and  organs.  These  cells  enter 
the  circulation  as  lymphocytes.  According  to  some,  the  mononuclear, 
transitional,  polymorphonuclear,  and  polynuclear  forms  are  later  stages 
in  the  development  of  these  cells.  According  to  others,  the  poly- 
morphonuclear and  polynuclear  forms  are  derived  from  the  myelocytes 
of  bone  marrow. 

The  origin  of  the  blood  platelets  is  not  known.  It  is  possible  that 
they  represent  extrusion  products  of  the  blood  cells. 

TECHNIC. 

(i)  Fresh  Blood. — Prick  a  finger  with  a  sterile  needle.  Touch  the  drop  of  blood 
to  the  centre  of  the  slide  and  cover  quickly.  For  immediate  examination  of  fresh 
blood  no  further  preparation  is  necessary.  Evaporation  may  be  prevented  by 
cementing,  or  by  smearing  a  rim  of  vaseline  around  the  cover-glass. 

(2)  Blood  Smears. — From  the  same  or  a  second  prick  take  up  a  drop  of  blood 
along  the  edge  of  a  mounting  slide.  Quickly  place  the  edge  against  the  surface  of 
a  second  slide  and  dravi^  the  edge  across  the  surface  in  such  a  manner  as  to  leave  a 
thin  film  or  smear  of  blood.  Allow  the  smear  to  become  perfectly  dry  and  stain  by 
technic  9,  p.  28.  By  this  method  the  acidophile  granules  are  stained  red,  baso- 
phile  granules  purple,  and  neutrophile  granules  a  reddish-violet. 

Good  results  may  also  be  obtained  by  fixing  the  dried  smear  for  half  an  hour 
in  equal  parts  alcohol  and  ether  and  staining  first  in  a  strong  alcoholic  solution  of 
eosin,  then  in  a  rather  weak  aqueous  solution  of  methylene  blue. 


CHAPTER  V. 

MUSCLE  TISSUE. 

While  protoplasm  in  general  possesses  the  property  of  contrac- 
tility, it  is  in  muscle  tissue  that  this  property  reaches  its  highest  de- 
velopment.    Moreover,  in  muscle  this  contractility  is  along  definite 


Fig.  50. — Isolated  Smooth  Muscle  Cells  from  Human  Small  Intestine.  X400.  (Tech- 
nic  I,  p.  109.)  Rod-shaped  nucleus  surrounded  by  area  of  finely  granular  protoplasm; 
longitudinal  striations  of  cytoplasm. 

directions,  and  is  capable  of  causing  motion,  not  only  in  the  cell  itself, 
but  in  structures  outside  the  cell. 

Muscle  may  be  classified  as:  (i)  Involuntary  smooth  muscle;  (2) 
voluntary  striated  muscle;  (3)  involuntary  striated  muscle  or  heart 
muscle. 

I.  Involuntary  Smooth  Muscle. — This  consists  of  long  spindle- 
shaped  cells  (Fig.  50).     The  length  of  the  cell  varies  from  30  to  200/'., 


C"^-i^ 


B 

Fig.  51. — Apparent  Intercellular  Bridges  of  Smooth  Muscle.  A,  From  longitudinal 
section  of  intestine  of  guinea-pig;  B,  from  transverse  section  of  intestine  of  rabbit.  X420. 
(2,  Nerve  cell;  h,  end  of  muscle  cell.     (Stohr.) 

its  width  from  3  to  8/(,  except  in  the  pregnant  uterus,  where  the  cells 
frequently  attain  a  much  greater  size.  At  the  centre  of  the  cell,  which 
is  its  thickest  portion,  is  a  long  rod-shaped  nucleus  surrounded  by  an 

101 


102  THE  TISSUES. 

area  of  finely  granular  cytoplasm.  The  rest  of  the  cytoplasm  shows 
delicate  longitudinal  striations,  which  probably  represent  a  longitu- 
dinal arrangement  of  the  spongioplasm.  The  cells  are  united  by  a 
small  amount  of  cement  substance.  Intercellular  "bridges"  similar 
to  those  connecting  epithelial  cells  have  been  described  (Fig.  51). 

Smooth  muscle  cells  may  be  arranged  in  layers  of  considerable 
thickness,  the  cells  having  a  definite  direction,  as  in  the  so-called 
"musculature"  of  the  intestine  (Fig.  52).  In  such  masses  of  smooth 
muscle  the  cells  are  separated  into  groups  or  bundles  by  connective 
tissue.  Smooth  muscle  cells  may  be  arranged  in  a  sort  of  network, 
the  cells  crossing  and  interlacing  in  all  directions,  as  in  the  wall  of  the 


Fig.  52. — Smooth  Muscle  from  Longitudinal  Section  of  Cat's  Small  Intestine,  show- 
ing Portions  of  Inner  Circular  and  Outer  Longitudinal  Muscle  Coats  with  Intervening 
Connective  Tissue.  X350.  (Technic  3,  p.  109.)  a,  Transversely  cut  cells  of  inner  circu- 
lar layer;  in  comparatively  few  has  the  plane  of  section  passed  through  the  nucleus;  b, 
longitudinally  cut  cells  of  outer  longitudinal  layer.  In  many  of  the  cells  the  plane  of  sec- 
tion has  not  passed  through  the  nucleus;  c,  intermuscular  septum  (connective  tissue);  d, 
small  artery. 

frog's  bladder.  Again,  they  may  be  scattered  in  small  groups  or  singly 
among  connective-tissue  elements,  as  in  the  villi  of  the  small  intestine. 

2.  Voluntary  Striated  Muscle. — This  consists  of  cylindrical 
fibres  from  50  to  130  mm.  in  length  and  from  10  to  100//  in  diameter. 

Each  muscle  fibre  consists  of  (a)  a  delicate  sheath,  the  sarcolemma, 
enclosing  {b)  the  muscle  substance  proper,  in  which  lie  (c)  the  muscle 
nuclei. 

The  sarcolemma  is  a  clear,  apparently  structureless,  membrane, 
which  adheres  so  closely  to  the  underlying  muscle  substance  as  to  be 
indistinguishable  in  most  preparations.  In  teased  specimens  it  may 
frequently  be  seen  at  the  torn  ends  of  the  fibres  (Fig.  53). 

The  muscle  substance  consists  of  ergastoplasm  {Jibrilla)  and  sarco- 


MUSCLE  TISSUE. 


103 


plasm,  and  shows  two  sets  of  striations  (Fig.  54),  longitudinal  striations 
and  cross  striations.  The  longitudinal  striations  are  due  to  parallel 
running  ultimate  fibrillcC,  of  which  the  muscle 
fibre  is  composed.  These  fibrillte  are  united  by 
a  minute  amount  of  interfibrillar  cement  sub- 
stance. The  transverse  striations  appear  in  the 
unstained  fibre  examined  by  reflected  light  as 
alternate  light  and  dark  bands  (Figs.  54  and  55). 
The  light  band  is  composed  of  a  singly  refracting 
(isotropic)  substance,  the  dark  band  of  a  doubly 
refracting  (anisotropic)  substance.  Through  the 
middle  of  the  light  band  runs  a  fine  dark  (aniso- 
tropic) line  {Kraiise's  line),  while  an  even  finer 
light  (isotropic)  line  {Hensen's  line)  runs  through 
the  middle  of  the  dark  band.  As  both  dark  and 
light  substances  run  through  the  entire  thickness 
of  the  fibre,  they  in  reality  constitute  discs  of 
muscle  substance  (Fig.  55).  By  means  of  certain 
chemicals  these  discs  may  be  separated,  the 
separation  taking  place  along  the  lines  of  Klrause. 
Each  "muscle  disc''  thus  consists  of  that  portion 
of  a  fibre  included  between  two  adjacent  lines  of 
Krause  and  is  composed  of  a  central  dark  disc, 
and  on  either  side  one-half  of  each  adjacent  light 
disc.  A  muscle  fibre  is  thus  seen  to  be  divisible 
longitudinally  into  ultimate  fihrillcB,  transversely 
into  muscle  discs.  What  is  known  as  the  sarcous 
element  of  Boicmaii  is  that  portion  of  a  single 
fibrilla  which  is  included  in  a  single  disc,  i.e.,  be-  Fig.  53.— Semidiagramma- 

,  ^  J.  ^  ,.  ^  T'  /T--  N  ^^^   Drawing  of  Parts  of 

tween  two  adjacent  Imes  of  Krause  (rig.  55). 


The  sarcoplasm  is  not  evenly  distributed 
throughout  the  fibre.  On  cross  section  irregular 
trabeculae  of  sarcoplasm  are  seen  extending  in 
from  the  sarcolemma  (Fig.  56). 


two  Muscle  Fibres  which 
have  been  broken,  show- 
ing the  relations  between 
Muscle  Substance  Proper 
and  Sarcolemma.  (Ran- 
vier.)  m,  a.  Retracted 
These  separate  ^"^1^  of  muscle  substance; 
,       .  .  between  which  is  seen  the 

the  fibrillce  mto  bundles,  the  muscle  columns  oj     sarcolemma  with  several 

KolUker.     A  transverse  section  of  one  of  these    -^^herent  muscle  nuclei: 

3.    thm   layer  of  muscle 

columns  presents  the  appearance  of  a  network  of    substance  which  has  ad- 

,  ,      ^  .  ^,     ...  ,  hered  to  the  sarcolemma: 

sarcoplasm  and  of  mterfibrillar  cement  substance  „,  muscle  nucleus:  5,  sar- 
enclosing  the  fibrillce.  This  appearance  is  known  ^-o'emma:  p  space  be 
as  Colinhcim's  field  (Figs.  55  and  56). 


tween    sarcolemma    and 
muscle  substance. 


10^ 


THE  TISSUES. 


The  contractile  element  of  the  fibre,  the  fibrilla,  is  anisotropic,  the 
sarcoplasm  isotropic;  the  former,  therefore,  appears  dark,  the  latter 
light  by  polarized  light.  Upon  this  is  based  Rollet's  theory  of  the 
structure  of  the  striated  muscle  fibre  (Fig.  57).  According  to  this 
theory,  each  fibrilla  consists  of  a  number  of  rod-shaped  segments 
joined  end  to  end.     Each  segment  consists  of  a  thicker  central  portion, 


I 


d  ► 


Fig. 


54- 


I'IG. 


Fig.  54. — Portion  of  Striated  Voluntary  Muscle  Fibre.  X350.  (Technic  4,  p.  log.) 
The  fibre  is  seen  to  be  marked  transversely  by  alternate  light  and  dark  bands.  Through 
the  centre  of  the  light  band  is  a  delicate  dark  line  (Krause's  line);  through  the  centre  of  the 
dark  band  a  fine  light  line  indicates  Hensen's  line.  The  black  line  outlining  the  fibre  repre- 
sents the  sarcolemma.     a,  Fibrillse;  h,  muscle  nucleus;  c,  Krause's  line;  d,  Hensen's  line. 

Fig.  55. — Diagram  of  Structure  of  a  Muscle  Column  of  KoUiker.  The  appearance 
presented  by  the  cross-cut  muscle  column  =  Cohnheim's  field,  a,  Muscle  fibrillae,  h,  sar- 
cous  element;  c,  Krause's  line;  d,  Hensen's  line;  e,  Cohnheim's  field;  /,  muscle  disc. 

which  tapers  almost  to  a  point  where  it  joins  the  next  adjacent  segment. 
The  point  of  union  is  marked  by  a  minute  globular  swelling.  Between 
the  fibrillae  is  the  semi-fluid  sarcoplasm.  In  the  formation  of  a  fibre 
similar  parts  of  each  fibril-segment  lie  in  the  same  transverse  plane. 
The  thicker  portions  lying  side  by  side  form  the  dark  disc  in  which 
there  is  comparatively  little  sarcoplasm.  The  attenuated  portions, 
with  their  relatively  large  amount  of  sarcoplasm,  form  the  light  disc. 
The  row  of  globular  swellings  forms  the  line  of  Krause. 


MUSCLE  TISSUE. 


105 


Two  varieties  of  striated  voluntary  muscle  fibres  are  distinguished, 
white  fibres  and  red  fibres.  The  difference  between  the  two  is  due 
to  the  amount  of  sarcoplasm — the  red  fibres  being  rich  in  sarcoplasm, 
the  white  fibres  poor.  Red  fibres  contract  less  rapidly  than  white, 
but  are  less  easily  fatigued.  In  man  white  fibres  are  in  the  large 
majority,  red  fibres  never  occurring  alone,  but  mingled  with  white 
fibres  in  some  of  the  more  active  muscles,  such  as  those  of  respiration 
and  mastication.  In  some  of  the 
lower  animals  are  found  muscles 
made  up  wholly  of  red  fibres.  H  H  H  H  H  H     I*  ^ 

Muscle   fibres   ending   within  the  ■■■■■■     J 

substance  of  a  muscle  have  pointed 
extremities.  Where  muscle  fibres  join 
tendon,   the  fibre  ends  in  a  rounded 


Fig.  s6. 


Fig. 


Fig.  56. — Semidiagrammatic  Drawing  of  Transverse  Section  of  a  Voluntary  Muscle 
Fibre,  showing  Sarcolemma;  sarcoplasm  separating  iibrils  into  bundles,  each  bundle  con- 
stituting a  muscle  column  of  Kolliker  and  the  appearance  of  its  cross-cut  end  being  Cohn- 
heim's  field,     a,  Sarcoplasm:  h,  Cohnheim's  fields;  c,  sarcolemma. 

Fig.  57.— Diagram  representing  Rollet's  Theory  of  the  Structure  of  a  \'oluntary  Mus- 
cle Fibre,     a,  Dark  disc;  6,  light  disc;  c,  sarcoplasm;  rf,  fibrilla;  e,  Krause's  line. 


or  blunt  extremity,  the  sarcolemma  being  continuous  with  the  tendon 
fibres  (Figs.  58  and  59). 

Muscle  fibres  are  usually  unbranched.  In  some  muscles — e.g., 
those  of  the  tongue  and  of  the  eye— anastomosing  branches  occur. 
When  muscle  fibres  end  in  mucous  membranes — e.g..  the  muscle  fibres 
of  the  tongue — their  terminations  are  often  branched. 

Muscle  fibres  are  multinuclear,  some  of  the  large  fibres  containing 
a  hundred  or  more  nuclei.  In  the  white  fibres  the  nuclei  are  situated 
at  the  periphery  just  beneath  llic  sarcolemma.  In  red  fil)rcs  they 
are  centrally  placed. 


106 


THE  TISSUES. 


3.  Involuntary  Striated  Muscle  (Heart  Muscle). — This  occu- 
pies an  intermediate  position,  both  morphologically  and  embryo- 
logically,  relative  to  smooth  muscle  and  to 
striated  voluntary  muscle.  Like  the  former,  it 
is  composed  of  cells.  Like  the  latter,  it  is  both 
longitudinally  and  transversely  striated.  Heart- 
muscle  cells  are  short,  thick  cylinders.  These 
are  joined  end  to  end  to  form  long  fibres.  By 
means  of  lateral  branches  the  cells  of  one  fibre 
anastomose  with  cells  of  adjacent  fibres.  Each 
heart-muscle  cell  usually  contains  one  nucleus; 
some  cells  contain  several  nuclei.  While  there  is 
no  distinct  sarcolemma,  the  sarcoplasm  is  more 
abundant  at  the  surface  of  the  cell,  thus  giving 
much  the  appearance  of  an  enclosing  membrane. 
The  amount  of  sarcoplasm  throughout  the  cell  is 
large.  Around  the  nucleus  is  an  area  of  sarco- 
])lasm  free  from  fibrillae.  This  area  often  ex- 
tends some  distance  toward  the  ends  of  the  cell. 
The  striations  of  heart  muscle  are  less  dis- 
tinct than  are  those  of  voluntary  muscle. 
According  to  McCallum,  they  represent  very 
similar  structures.  The  longitudinal  striations 
indicate  fibrillcE-  united  by  cement  substance. 
From  the  central  mass  of  sarcoplasm  which 
surrounds  the  nucleus,  strands  radiate  tpward 
the  periphery.  These  strands,  anastomosing, 
separate  the  fibrillae  into  columns,  the  muscle 
columns  of  Kolliker.  In  cross  section  these  pre- 
sent the  appearance  described  under  voluntary 
Fig.    58.— Semidiagram-    muscle  as  Cohnheim'' s  fields.     The  disposition  of 

matic     Illustration     of  ,.  i     j-  .li 

Endings  of  Muscle  Fi-  the  sarcoplasm,  cxtcndmg  outward  irom  the 
bres  vvithin  a  Muscle    j-egion  of  the  nuclcus  like  the  spokes  of  a  wheel, 

and  in  1  endon.  (Cjage.)  °  _  ... 

a,  Tapering  end  of  fibre  gives  to  the  cross  section  a  characteristic  radiate 
':::^^:1^Sl  appearance  (Fig.  61).  The  transverse  markings 
of    the    central    fibre    represent,  as  in  voluntary  muscle,  alternate  light 

shows  the  same  method  ,      ,      ,       ,.  rr^,  ,        ,  •  ^  ^^  r      i 

of  termination;  c,  c,  and  dark  dtscs.  1  hrough  the  middle  or  the 
each  fibre  terminates  j|  i^  ^^^^  ^^^  -^^  ^^^^  ^-^^  membrane  of  Krause. 
above  in  pointed  intra-        "  -' 

muscular  ending,  below  McCallum  describes  Krause's  membrane  as 
nected  with  tendon  '       belonging  not  Only  to  the  fibrillar  element,  but 


MUSCLE  TISSUE. 


107 


also  to  the  sarcoplasm.  The  latter  he  describes  as  further  subdivided 
by  membranes,  which  are  transversely  continuous  with  Krause's 
membranes,  into  minute  discs.  The  centre  of  the  cell  around  the 
nucleus  is  wholly  composed  of  these  little  discs  of  sarcoplasm. 

McCallum  describes  two  appearances  which  the  lines  of  union 
between  the  muscle  cells  present.  In  one  each  fibrilla  shows  a  thick- 
enincT  at  the  cement  line,  from  which  one  or  more  delicate  filaments 


I  I 


I  I 


S  T'S. 


Fig.  59. 


Fig.  60. 


Fig.  59. — Two  Muscle  Fibres  from  Upper  End  of  Human  Sartorius,  to  show  connection 
of  muscle  and  tendon.      X350.     (Gage.)     ?»,  Muscle  fibres: /,  tendon  fibres. 

Fig.  60. — Muscle  Cells  from  the  Human  Heart  (technic  6,  p.  no),  showing  lateral 
branches  and  lines  of  union  between  cells.      X  soo. 


cross  the  cement  to  unite  with  similar  filaments  from  an  opposite 
fibrilla.  In  the  other  form  of  union  the  cement  substance  is  crossed 
by  intercellular  bridges  similar  to  those  described  under  epithelium. 

Recent  investigations  tend  to  prove  that  what  have  been  described 
as  heart-muscle  cells  are  not  separate  units,  but  that  heart  muscle  is 
a  syncytial  tissue,  each  cell  representing  only  a  groicth  segment  of 
the  whole  muscle  fibre.  The  occurrence  of  non-nucleated  segments 
and  the  fact  that  the  longitudinal  fibrillae  are  described  by  some  ob- 
servers as  passing  uninterruptedly  through  the  "intercellular"  cement 
substance  favor  this  view.  On  the  other  hand,  the  ease  with  which 
heart  muscle  may  be  separated  into  cells,  especially  in  young  animals 


108  THE  TISSUES. 

and  in  the  lower  vertebrates,  and  the  definite  staining  reaction  which 
intercellular  substance  gives  when  subjected  to  the  action  of  silver 
nitrate  are  in  favor  of  a  cellular  structure. 

Development  of  Muscle  Tissue. 

In  the  higher  animals  muscle  tissue,  with  the  single  exception  of 
the  sweat-gland  muscles  (page  62),  is  derived  wholly  from  mesoderm. 

The  smooth  muscle  cell  shows  the  least  differentiation.  In  be- 
coming a  smooth  muscle  cell  the  embryonal  cell  changes  its  shape, 


-  ^ 


C5i 


Fig.  61. — Section  of  Heart  Muscle.  X350.  (Technic  7,  p.  no.)  a,  Cells  cut  longi- 
tudinally; b,  cells  cut  transversely  (only  three  nuclei  have  been  included  in  the  plane  of 
section);  c,  cells  cut  obliquely;  d,  connective-tissue  septum. 

becoming  greatly  elongated,  while  at  the  same  time  its  spongioplasm 
is  arranged  as  longitudinally  disposed  contractile  fibrils. 

A  voluntary  muscle  fibre  is  a  highly  differentiated  multinuclear 
cell  or  syncytium.  Each  fibre  is  developed  from  a  single  cell  (myo- 
blast) of  one  of  the  embryonic  muscle  segments  or  myotomes.  These 
cells,  which  are  at  first  spherical,  become  elongated  and  spindle- 
shaped.  The  nucleus  is  at  this  stage  centrally  placed,  and  the  spongio- 
plasm occurs  in  the  form  of  a  reticulum.  Regular  arrangement 
of  the  spongioplasm  first  appears  around  the  periphery,  while  the 
central  portion  of  the  cell  is  still  occupied  by  reticular  spongioplasm 
and  the  nucleus.  The  fibrils  extend  toward  the  centre  until  they 
fill  the  entire  cell,  which  has  now  become  a  muscle  fibre.  During 
this  process  of  fibrillation  the  nucleus  has  been  undergoing  mitotic 


MUSCLE  TISSUE.  109 

division.  In  the  white  fibres  these  nuclei  migrate  to  the  surface  and 
come  to  lie  just  beneath  the  sarcolemma.  The  cement  substance 
which  unites  the  fibrils,  as  well  as  the  larger  masses  of  sarco- 
plasm,  represents  the  remains  of  still  undifferentiated  protoplasm 
(hyaloplasm). 

McCallum  describes  the  development  of  heart  muscle  in  the  pig 
as  follows:  In  embryos  lo  mm.  long  the  heart  muscle  consists  of 
closely  packed  spindle-shaped  cells,  each  containing  an  oval  nucleus. 
The  spongioplasm  is  arranged  in  the  form  of  a  network,  no  fibrils 
being  present.  In  embryos  25  mm.  long  the  shape  of  the  cell  re- 
mains unchanged,  but  on  cross  section  there  can  be  seen  around  the 
periphery  a  row  of  newly  formed  fibril  bundles  which  have  developed 
from  the  spongioplasm.  From  the  periphery  fibril  bundles  spread 
toward  the  centre.  In  embryos  70  mm.  long  the  heart-muscle  cell 
has  assumed  its  adult  shape  and  structure. 

Attention  has  already  been  called  (page  47)  to  the  spongioplasm 
as  the  contractile  element  of  protoplasm.  It  is  to  be  noted  that  in  the 
development  of  muscle  no  new  element  appears,  the  contractile  fihriUcE 
representing  nothing  more  than  a  specialization  of  the  already  contractile 
spongioplosm. 

TECHNIC. 

(i)  Isolated  Smooth  Muscle  Cells. — Place  small  pieces  of  the  muscular  coat  of 
the  intestine  in  o.i-per-cent.  aqueous  solution  of  potassium  bichromate,  or  in  30-per- 
cent, alcohol  for  forty-eight  hours.  Small  bits  of  the  tissue  are  teased  thoroughly 
and  mounted  in  glycerin.  Nuclei  may  be  demonstrated  by  first  washing  the  tissue 
and  then  staining  for  twelve  hours  in  alum  carmine  (page  17).  This  is  poured  off, 
the  tissue  again  washed  in  water  and  preserved  in  eosin-glycerin,  which  gives  a 
pink  color  to  the  cytoplasm. 

(2)  Potassium  hydrate  in  40-per-cent.  aqueous  solution  is  also  recommended  as 
a  dissociater  of  smooth  muscle  cells.  Pieces  of  the  muscular  coat  of  the  intestine 
are  placed  in  this  solution  for  five  minutes,  then  transferred  to  a  saturated  aqueous 
solution  of  potassium  acetate  containing  i-per-cent.  hydric  acetate  for  ten  minutes. 
Replace  the  acetate  solution  by  water,  shake  thoroughly,  allow  to  settle,  pour  off 
water,  and  add  alum-carmine  solution  (page  17).  After  twelve  hours'  staining, 
wash  and  transfer  to  eosin-glycerin. 

(3)  Sections  of  Smooth  Muscle. — Fix  small  pieces  of  intestine  in  formalin- 
Miiller's  (technic  5,  p.  7)  or  in  Zenker's  fluid  (technic  9,  p.  8).  Thin  transverse  or 
longitudinal  sections  are  stained  with  ha^motoxylin-eosin  (technic  i,  p.  18),  and 
mounted  in  balsam.  As  the  two  muscular  coats  of  the  intestine  run  at  right  angles 
to  each  other,  both  longitudinally  and  transversely  cut  muscle  may  be  studied  in 
the  same  section. 

(4)  Striated  \'oluntary  Aluscle  Fibres. — One  of  the  long  muscles  removed  from 


no  THE  TISSUES. 

a  recently  killed  animal  is  kept  in  a  condition  of  forced  extension  while  a  i-per- 
cent.  aqueous  solution  of  osmic  acid  is  injected  into  its  substance  at  various  points 
by  means  of  a  hypodermic  syringe.  Fixation  is  accomplished  in  from  three  to  five 
minutes.  The  parts  browned  by  the  osmic  acid  are  then  cut  out  and  placed  in  pure 
glycerin,  in  which  they  are  teased  and  mounted. 

(5)  Sections  of  Striated  Voluntary  Muscle. — Fix  a  portion  of  a  tongue  in  forma- 
lin-Miiller's  fluid  or  in  Zenker's  fluid  (page  8).  Thin  sections  are  stained  with 
haematoxylin-picro-acid-fuchsin  (technic  3,  p.  19)  and  mounted  in  balsam.  As  the 
muscle  fibres  of  the  tongue  run  in  all  directions,  fibres  cut  transversely,  longitudi- 
nally, and  obliquely  may  be  studied  in  the  same  section.  The  sarcolemma,  the 
pointed  endings  of  the  fibres,  and  the  relation  of  the  fibres  to  the  connective  tissue 
can  also  be  seen. 

(6)  Isolated  heart-muscle  cells  may  be  obtained  in  the  same  manner  as  smooth 
muscle  cells.      (See  technic  i,  p.  109.) 

(7)  Sections  of  Heart  Muscle. — These  are  prepared  according  to  technic  3 
(above).  By  including  the  heart  wall  and  a  papillary  muscle  in  the  same  section, 
both  longitudinally  and  transversely  cut  cells  are  secured.  The  stain  may  be  either 
haematoxylin-eosin  (technic  i,  p.  18),  or  hasmatoxylin-picro-acid-fuchsin  (technic 
3,  P-  19)- 


CHAPTER  VI. 
NERVE  TISSUE. 

The  Neurone. 

In  most  of  the  cells  thus  far  described  the  protoplasm  has  been 
confined  to  the  immediate  vicinity  of  the  nucleus.  In  the  smooth 
muscle  cell  was  seen  an  extension  of  protoplasm  to  a  considerable 
distance  from  the  nuclear  region,  while  in  the  connective-tissue  cells 
of  the  cornea  the  protoplasmic  extensions  took  the  form  of  distinct 
processes.  Processes,  often  extending  long  distances  from  the  cell 
body  proper,  constitute  one  of  the  most  striking  features  of  nerve- 
cell  structure.  Some  of  these  processes  are  known  as  nerve  fibres; 
and  nerve  tissue  was  long  described  as  consisting  of  two  elements, 
nerve  cells  and  nerve  fibres.  With  the  establishment  of  the  unity  of 
the  nerve  cell  and  the  nerve  fibre,  the  nerve  cell  with  its  processes 
was  recognized  as  the  single  structural  unit  of  nerve* tissue.  This 
unit  of  structure  is  known  as  a  neurone.  The  neurone  may  thus  be 
defined  as  a  nerve  cell  with  all  of  its  processes. 

In  the  embryo  the  neurone  is  developed  from  one  of  the  ectoder- 
mic  cells  which  constitute  the  wall  of  the  primitive  neural  canal. 
This  embryonic  nerve  cell,  or  neuroblast,  is  entirely  devoid  of  proc- 
esses. Soon,  however,  from  one  end  of  the  cell  a  process  begins  to 
grow  out.  This  process  is  known  as  the  axone  (axis-cylinder  process, 
neuraxone,  neurite).  Other  processes  appear,  also  as  outgrowths  of 
the  cell  body;  these  are  known  as  protoplasmic  processes  or  dendrites. 

Each  adult  neurone  thus  consists  of  a  cell  body,  and  passing  oft" 
from  this  cell  body  two  kinds  of  processes,  the  axis-cylinder  process 
and  the  dendritic  processes  (Fig.  62). 

I.  The  Cell  Body. — Like  most  other  cells,  the  nerve  cell  body 
consists  of  a  mass  of  protoplasm  surrounding  a  nucleus  (Fig.  63). 
Nerve  cell  bodies  vary  in  size  from  very  small  cell  bodies,  such  as 
those  found  in  the  granule  layers  of  the  cerebellum  and  of  the  olfac- 
tory lobe,  to  the  large  bodies  of  the  Purkinje  cells  of  the  cerebellum 
and  of  the  motor  cells  of  the  \'cnlral  horns  of  the  cord,  wliich  are 
among  the  largest  in  the  body.     There  is  as  much  \ariation  in  shape 

111 


112 


THE  TISSUES. 


as  in  size,  and  some  of  the  shapes  are  characteristic  of  the  regions  in 
which  the  cells  are  situated.  Thus,  many  of  the  bodies  of  the  cells 
of  the  spinal  ganglia  are  spheroidal;  of  most  of  the  cells  of  the  cortex 

cerebri,  pyramidal;  of  the  cells  of  Pur- 
kinje,  pyriform;  of  the  cells  of  the 
ventral  horns  of  the  cord,  irregularly 
stellate.  According  to  the  number  of 
processes  given  off,  nerve  cells  are  often 
referred  to  as  unipolar,  bipolar,  or 
multipolar. 


/, 


w 


b  ~ 


Fig.  62. 


Fig.  6- 


FiG.  62. — Scheme  of  Lower  Motor  Neurone.  (Barker.)  The  cell  body,  protoplasmic 
processes,  axone,  collaterals,  and  terminal  arborizations  in  muscle  are  all  seen  to  be  parts 
of  a  single  cell  and  together  constitute  the  neurone,  c,  Cytoplasm  of  cell  body  containing 
chromophihc  bodies,  neurofibrils,  and  perifibrillar  substance;  n,  nucleus;  n',  nucleolus;  d, 
dendrites;  ah,  axone  hill  free  from  chromophilic  bodies;  ax,  axone;  sf,  branch  (collateral); 
m,  medullary  sheath;  n  R,  node  of  Ranvier  where  branch  is  given  off;  si,  neurilemma  (prob- 
ably not  present  in  central  nervous  system);  m',  striated  muscle  fibre;  tel,  motor  end  plate. 

Fig.  63. — Large  Motor  Nerve  Cell  from  Ventral  Horn  of  Spinal  Cord  of  Ox,  showing 
Chromophilic  Bodies.  (From  Barker,  after  von  Lenhossek.)  a,  Pigment;  b,  axone; 
c,  axone  hill;  d,  dendrites. 


The  NUCLEUS  of  the  nerve  cell  (Fig.  63)  differs  in  no  essential 
from  the  typical  nuclear  structure.  It  consists  of  (i)  a  nuclear  mem- 
brane, (2)  an  intranuclear  network  of  linin  and  chromatin,  (3)  an 
achromatic  nucleoplasm,  and  (4)  a  nucleolus. 

The  CYTOPLASM  of  the  nerve  cell  consists  of  two  distinct  elements: 


XER\'E  TISSUE. 


113 


(i)  Neurofibrils,  and  (2)  perifibrillar  substance.     In  most  nerve  cells 
a  third  element  is  present,  (3)  chromophilic  bodies. 

(i)  The  neurofibrils  are  extremely  delicate  fibrils  which  are  con- 
tinuous throughout  the  cell  body  and  all  of  its  processes.  Within 
the  body  of  the  cell  they  cross  and  interlace  and  probably  anastomose 
(Figs.  64  and  65). 


^ 


/V'l 


} 


Fig.  64. — Ganglion  Cells,  Stained  by  Bethe's  Method,  showing  Neurofibrils.  A, 
Anterior  horn  cell  (human);  B,  cell  from  facial  nucleus  of  rabbit;  C,  dendrite  of  human 
anterior  horn  cell  showing  arrangement  of  neurofibrils.     (Bethe.) 


(2)  The  perifibrillar  substance  (Fig.  64)  is  a  fluid  or  semifluid 
substance  which  both  in  the  cell  body  and  in  the  processes  surrounds 
and  separates  the  neurofibrils.  It  is  believed  by  some  to  be  like 
the  fibrils,  continuous  throughout  cell  body  and  processes,  by  others  to 
be  interrupted  at  certain  points  in  the  axone  (see  page  121). 

(3)  The  chromophilic  bodies  (Fig.  63)  are  granules  or  groups  of 


114 


THE  TISSUES. 


granules  which  occur  in  the  cytoplasm  of  all  of  the  larger  and  of  many 
of  the  smaller  nerve  cells.  They  are  best  demonstrated  by  means 
of  a  special  technic  known  as  the  method  of  Nissl  (page  35).  When 
subjected  to  this  technic,  nerve  cells  present  two  very  different  types 
of  reaction.  In  certain  small  cells  the  amount  of  cytoplasm  is  ex- 
tremely small  and  only  the  nuclei  stain.  Such  cells  are  found  in  the 
granule  layers  of  the  cerebellum,  olfactory  lobe,  and  retina.  They 
are  known  as  caryochromes,  and  apparently  consist  wholly  of  neurofibrils 


Fig.  65. — Body  of  Large  Pyramidal  Cell  from  Cortex  of  Cat.  Silver  Method  of 
Cajal.  Shows  nucleus  pale  and  arrangement  of  neurofibrils  within  the  cell;  a,  axone; 
b,  main  or  apical  dendrite.     (Cajal). 

and  perifibrillar  substance.  Other  cells  react,  both  as  to  their  nuclei 
and  as  to  their  cell  bodies,  to  the  Nissl  stain.  These  cells  are  known 
as  somatochromes.  Taking  as  an  example  of  this  latter  type  of  cell 
one  of  the  motor  cells  of  the  ventral  horn  of  the  cord  and  subjecting  it 
to  the  Nissl  technic,  we  note  that  the  cytoplasm  is  composed  of  two 
distinct  elements:  {a)  a  clear,  unstained  ground  substance,  and,  scat- 
tered through  this,  {h)  deep-blue-staining  masses,  the  chromophilic 
bodies  (Fig.  63).  These  bodies  are  granular  in  character  and  differ  in 
shape,  size,  and  arrangement.     They  may  be  large  or  small,  regular 


NER^'E  TISSUE. 


llo 


or  irregular  in  shape,  may  be  arranged  in  rows  or  in  an  irregular 
manner,  may  be  close  together,  almost  filling  the  cell  body,  or  quite 
separated  from  one  another.  Presenting  these  variations  in  different 
types  of  cells,  the  appearance  of  the  chromophilic  bodies  in  a  partic- 
ular type  of  cell  remains  constant,  and  has 
thus  been  used  by  Nissl  as  a  basis  of  classi- 
fication.' 

It  is  important  to  note  in  studying  the 
nerve  cell  by  this  method  that  somato- 
chrome  cells  of  the  same  type  frequently 
show  marked  variations  in  staining  in- 
tensity. This  appears  to  depend  upon  the 
size  and  closeness  of  arrangement  of  the 
chromophilic  bodies,  and  this  again  seems 
dependent  upon  changes  in  the  cytoplasm 
connected  with  functional  activity. 

In  cells  stained  by  Nissl's  method  the 
cytoplasm  between  the  chromophilic  bodies 
remains  unstained  and  apparently  struc- 
tureless, and  it  is  this  part  of  the  cytoplasm 
that  corresponds  to  the  neurofibrils  and 
perifibrillar  substance. 

The  relation  which  the  appearance  of  the 
Nissl-stained  cell  bears  to  the  structure  of  the 
living  protoplasm  is  still  undetermined.  According 
to  some  investigators  the  Nissl  bodies  exist  as  such 
in  the  living  cell.  Others  believe  that  they  are  not 
present  in  the  living  cell,  but  represent  precipitates 
due  either  to  postmortem  changes  or  to  the  action 
of  fixatives.  The  significance  of  the  Nissl  picture 
from  the  standpoint  of  pathology  lies  in  the  fact 
that  when  subjected  to  a  given  technic,  a  particular 
type  of  nerve  cell  always  presents  the  same  ap- 
pearance, and  that  this  appearance  furnishes  a 
norm  for  comparison  with  cells  showing  patho- 
logical changes,  and  which  have  been  subjected  to  the  same  Icchnic 


Fig.  66. — Pyramidal  Cell  from 
Human  Cerebral  Cortex. 
(Golgi  bichlorid  method. 
See  2,  p.  33.)  Golgi  cell  type 
I.  a,  Cell  body;  h,  main  or 
apical  dendrite  showing  gem- 
mules;  c,  lateral  dendrites 
showing  gemmules;  d,  a.xone 
with  collaterals.  Only  part 
of  a.xone  is  included  in 
drawing. 


Many  nerve  cells  contain  more  or  less  brownish  or  yellowish  pig- . 
ment  (Fig.  63).     This  pigment  is  not  present  in  the  cells  of  the  new- 
born, but  appears  in  increasing  amounts  with  age.     Its  significance 
is  not  known. 

'For  this  classification,  the  significance  of  which  is  somewhat  doubtful,  the  reader  is 
referred  to  Barker,   "The  Nervous  System  and  Its  Constituent  Neurones."  p.  121. 


116  THE  TISSUES. 

In  addition  to  its  characteristic  structure,  the  nerve  cell  may  con- 
tain many  elements  found  in  other  cells  (p.  39).  Golgi,  Holmgren, 
and  others  have  also  demonstrated  a  network  of  canals  v^ithin  the 
nerve  cell  similar  to  that  found  in  other  cells  (p.  42,  Fig.  4). 

II.  The  Protoplasmic  Processes  or  Dendrites. — These  have  a 
structure  similar  to  that  of  the  cell  body,  consisting  of  neurofibrils, 
perifibrillar  substance,  and,  in  somatochrome  cells,  chromophilic 
bodies  (Figs.  63  and  64).     Dendrites  branch  dichotomously,  become 


Fig.  67. — Golgi  Cell  Type  II.  from  Cerebral  Cortex  of  Cat.  (KoUiker.)  x,  Coarse 
protoplasmic  processes  with  gemmules  easily  distinguishable  from  the  more  delicate, 
smoother  axone,  a.  The  latter  is  seen  breaking  up  into  a  rich  plexus  of  terminal  fibres 
near  its  cell  of  origin,  practically  the  entire  neurone  being  included  in  the  drawing. 

rapidly  smaller,  and  usually  end  at  no  great  distance  from  the  cell  body 
(Figs.  66  and  67). 

III.  The  Axone. — This  differs  from  the  cell  body  and  dendrites  in 
that  it  contains  no  chromophilic  bodies  (Fig.  63),  consisting  wholly 
of  neurofibrils  and  perifibrillar  substance.  Not  only  is  it  entirely 
achromatic  itself,  but  it  always  takes  origin  from  an  area  of  the  cell 
body,  the  axone  hill  (Fig.  63),  which  is  free  from  chromophilic  bodies. 
It  is  as  a  rule  single,  and  while  usually  arising  from  the  body  of  the 
cell  may  be  given  off  from  one  of  the  larger  protoplasmic  trunks. 
Some  few  cells  have  more  than  one  axone,  and  nerve  cells  without 


NERVE  TISSUE.  117 

axones  have  been  described.  In  Golgi  preparations  the  axone  is 
distinguished  by  its  straighter  course,  more  uniform  diameter,  and 
smoother  outHne  (Fig.  66).  It  sends  off  few  branches  {collaterals), 
and  these  approximately  at  right  angles.  Both  axone  and  collaterals 
usually  end  in  terminal  arborizations.  In  most  cells  the  axone  ex- 
tends a  long  distance  from  the  cell  body.  Such  cells  are  known  as 
Golgi  cell  type  I.  (Fig.  66).  In  others  the  axone  branches  rapidly 
and  ends  in  the  gray  matter  in  the  vicinity  of  its  cell  of  origin — Golgi 
cell  type  II.  (Fig.  67). 

As  they  leave  the  cell  body  the  neurofibrils  of  the  axone  converge 
to  a  very  narrow  portion  of  the  axone,  where  the  perifibrillar  sub- 
stance is  much  reduced  in  amount,  or  according  to  some,  entirely 
interrupted.  Beyond  this  the  fibrils  become  more  separated  and 
the  perifibrillar  substance  more  abundant. 

Some  axones  pass  from  their  cells  of  origin  to  their  terminations 
as  "naked"  axones,  i.e.,  uncovered  by  any  sheath.  Other  axones 
are  enclosed  by  a  thin  membrane,  the  neurilemma  or  sheath  oi  Schwann. 
Still  others  are  surrounded  by  a  sheath  of  considerable  thickness 
known  as  the  medullary  sheath. 

Depending  upon  the  presence  or  absence  of  a  medullary  sheath, 
axones  may  thus  be  divided  into  two  main  groups — medullated  axones 
and  non-mediillated  axones. 

1.  NoN-MEDULLATED  AxoNES  (non-mcdullatcd  nerve  fibres)  (Fig. 
68).  These  are  subdivided  into  non-medullated  axones  without  a 
neurilemma  and  non-medullated  axones  with  a  neurilemma. 

{a)  Non-medullated  axones  without  a  neurilemma  are  merely  naked 
axones.  Present  in  large  numbers  in  the  embryo,  they  are  in  the 
adult  confined  to  the  gray  matter  and  to  the  beginnings  and  endings 
of  sheathed  axones,  all  of  the  latter  being  uncovered  for  a  short  dis- 
tance after  leaving  the  nerve  cell  body,  and  also  just  before  reaching 
their  terminations. 

(6)  Non-medullated  axones  with  a  neurilemma— Jibres  of  Remak 
(Fig.  68) .  In  these  the  axone  is  surrounded  by  a  delicate  homogeneous, 
nucleated  sheath,  the  neurilemma  or  sheath  of  Schwann  (see  p.  119). 
These  axones  are  described  by  some  writers  as  ha^■ing  no  true  neuri- 
lemma, but  merely  a  discontinuous  covering  of  flat  connective-tissue 
cells,  which  wrap  around  the  axone  and  correspond  to  the  endoneu- 
rium  of  the  nerve  trunk  (see  page  382). 

2.  Medullated  Axones  (medullated  nerve  fibres). — These,  like 
the  non-medullated,  are  subdivided  according  to  the  presence  or  ab- 


lis 


THE  TISSUES. 


sence  of  a  neurilemma  into  medullated  axones  with  a  neurilemma 
and  medullated  axones  without  a  neurilemma. 

(a)  Medullated  axones  with  a  neurilemma  constitute  the  bulk  of 
the  fibres  of  the  cerebro-spinal  nerves.  Each  fibre  consists  of  (i) 
an  axone,  (2)  a  medullary  sheath,  and  (3)  a  neurilemma. 

(i)  The  axone  is  composed  of  neurofibrils  continuous  with  those  of 
the  cell  body,  and  like  them  lying  in  a  perifibrillar  substance  or  neuro- 


FiG.  6S.  Fig.  69 

Fig.  68. — Non-medullated  Nerve  Fibres  with  Neurilemma,  only  the  nuclei  of  which 
can  be  seen.      X300. 

Fig.  69. — A,  Fresh  nerve  fibre  from  sciatic  nerve  of  rabbit  teased  apart  in  normal  salt 
solution,  showing  broad  unshrunken  axone  and  comparatively  thin  medullary  sheath. 
B,  Showing  crenation  of  medullary  sheath  which  occurs  soon  after  placing  fibres  in  salt 
solution.  C,  Same  after  fixation  and  staining  with  picro-acid-fuchsin,  showing  shrunken 
axone  and  broad  medullary  space.  The  latter  usually  contains  irregular  clumps  of 
myelin,     a.  Node  of  Ranvier;  b,  incisures  of  Schmidt;  c,  nucleus  of  neurilemma. 

plasm  (Fig.  72).  In  the  fresh  condition  the  axone  is  broad,  and  shows 
faint  longitudinal  striations  corresponding  to  the  neurofibrils,  or  ap- 
pears homogeneous  (Fig.  69,  A).  Fixatives  usually  cause  the  axone  to 
shrink  down  to  a  thin  axial  thread,  whence  its  older  name  of  axis- 
cylinder  (Fig.  6g,C).  A  delicate  membrane  has  been  described  by 
some  as  enveloping  the  axone.  It  is  known  as  the  axolemma  or  peri- 
axial sheath  (Fig.  70). 


XER\-E  TISSUE. 


119 


(2)  The  medullary  sheath  (Figs.  69  and  72)  is  a  thick  sheath  com- 
posed of  a  semifluid  substance  resembling  fat  and  known  as  mye- 
lin. In  the  fresh  state  the  myelin 
has  a  glistening  homogeneous  ap-  f 
pearance.  It  is  not  continuous,  but  ,  ^... 
is  divided  at  intervals  of  from  80  to 
6oo/(  by  constrictions,  the  nodes  or 
constrictions  of  Ranvier.  That  por- 
tion of  a  fibre  included  between  two 
nodes  is  known  as  an  internode  (Fig. 
70).  The  length  of  the  internode  is 
usually  proportionate  to  the  size  of 
the  fibre,   the  smaller  fibres  having 

the    shorter    internodes.       In    fresh     '  j      ,  1  fv 

specimens  the  medullary  sheath  of 
an  internode  appears  continuous 
(Fig.  69,  ^4),  but  in  fixed  specimens 
it  is  broken  up  into  irregular  seg- 
ments, Schniidt-Lantermann  segments, 
by  clefts  which  pass  from  neurilemma 
to  the  axolemma  or  axone,  and  are 
known  as  the  clefts  or  incisures  of 
Schmidt-Lantermann  (Fig.  69,  C). 
On  boiling  medullated  nerve  fibres 
in  alcohol  and  ether  a  fine  network  is 
brought  out  in  the  m^edullary  sheath, 
the  neurokeratin  network.  Owing  to 
the  resistance  of  neurokeratin  to  the 
action  of  trypsin,  it  has  been  con- 
sidered as  possibly  similar  in  compo- 
sition to  horn. 

(3)  The  neurilemma  or  sheath  of 
Schwann  (Figs.  70,  B,  and  72)  is  a 
delicate  structureless  membrane  Fig.  71 
which  encloses  the  myelin.  At  the 
nodes  of  Ranvier  the  neurilemma 
dips  into  the  constriction  and  comes 
in  contact  with  the  axone  or  axo- 
lemma. Against  the  inner  surface  of  the  neurilemma,  usuallv  about 
midway  l^ctwcen  two  nodes,  is  an  o^"al-shaped  nucleus,  the  nucleus  of 


Fig.   70.  Fig.   71. 

Fig.  70. — Diagram  of  Structure  of  a  Med- 
ullated Nerve  Fibre  of  a  Peripheral 
Nerve  showing  two  different  views  as  to 
relations  of  neurilemma  and  axolemma 
and  their  behavior  at  the  nodes  of 
Ranvier.  (Szymonowicz.)  a,  Neuro- 
tibrils;  /),  cement  substance;  r,  axone; 
d,  incisure  of  Schmidt;  e.  nucleus  of 
neurilemma;  /,  medullary  sheath;  g, 
sheath  of  Schwann;  h,  a.xone;  /,  a.xo- 
lemma;  f,  sheath  of  Schwann;  k,  node 
of   Ranvier. 

-Piece  of  ^fedullaled  Nerve 
from  Human  Radial  Nerve. 
X400.  Osmic-acid  fixation  and  stain. 
(Szymonowicz.)  a.  Medullary  sheath; 
/),  a.xone;  c,  sheath  of  Henle;  </,  nuclei 
of  Henle's  sheath;  e,  nucleus  of  neuri- 
lemma. 


120 


THE  TISSUES. 


the  neurilemma  (Figs.  69,  C,  and  71).     Each  nucleus  is  surrounded  by 
an  area  of  granular  protoplasm,  and  makes  a  little  depression  in  the 
myelin  and  a  slight  bulging  of  the  neurilemma  (Fig.  69,  C).     Accord- 
ing to  most  observers  no  neurilemma  is 
B  present  in  the  central  nervous  system. 

An  important  exception  is  Cajal,  who 
describes  the  medullated  fibre  of  the 
central  nervous  system  as  having  a 
neurilemma. 

In  addition  to  the  above-described 
sheaths,  most  medullated  fibres  of  per- 
ipheral nerves  have,  outside  the  neuri- 
lemma, a  nucleated  sheath  of  connect- 
ive-tissue origin,  known  as  the  sheath 
of  Henle  (Fig.  71). 


sp 


le 


pa 


gs 


sg 


n 
sz 


Two  views  as  to  the  relation  of  the  axolemma 
to  the  neurilemma  are  illustrated  in  Fig.  70. 
According  to  one  the  neurilemma  is  continuous, 
merely  dipping  into  the  nodes  of  Ranvier, 
where  it  touches  the  axolemma  or  the  axone. 
According  to  the  second  both  neurilemma  and 
axolemma  are  interrupted  at  the  node,  but 
unite  with  each  other  there  to  enclose  completely 
the  medullary  substance  of  the  internode. 


Fig.  72. — Scheme  of  Structure  of  Medullated  Per- 
ipheral Nerve  Fibre  of  a  Fish  (Nemiloff).  A, 
Cross  section;  B,  longitudinal  section;  on  left,  fibre 
is  shown  as  stained  intra  vitam  with  methylene 
blue;  on  right,  myelin  is  shown  black  as  in  osmic 
acid  staining,  with  the  incisures  of  Schmidt  in- 
dicated; sz,  cells  of  sheath  of  Schwann;  n,  their 
nuclei;  ss,  sheath  of  Schwann;  sp,  processes  of 
the  cells  of  sheath  of  Schwann  or  the  myelin 
sheath  network;  le,  larger  trabeculae  of  proto- 
plasmic framework  of  medullary  sheath  arranged 
obliquely  to  axis-cylinder  and  forming  the  so- 
called  "funnels";  leo,  clear  streaks  in  fibres 
treated  with  osmic  acid,  corresponding  to  le,  in- 
cisures of  Schmidt;  mo,  myelin  blackened  with 
osmic  acid;  ax,  axis-cylinder;  pa,  periaxial  space 
around  axis-cylinder;  gs,  "coagulum  sheath," 
granules  probably  representing  coagulated  fluid 
in  periaxial  space;  pf,  peripheral,  non-fibrillar, 
part  of  axis-cylinder;  /,  neurofibrils  of  axis- 
cylinder;  r,  ring-like  thickening  of  Schwann's 
sheath  at  node  of  Ranvier;    o,  cavity  in  r. 


NERVE  TISSUE.  il'l 

According  to  the  views  illustrated  in  Fig.  72,  that  part  of  the  axone  which  lies 
between  two  nodes  is  enveloped  by  a  cell,  or  by  several  cells  forming  a  syncytium. 
The  outer  homogeneous  membrane  there  pictured  would  thus  be  of  the  nature  of  a 
cell  membrane  or  cuticle,  and  would  correspond  to  the  neurilemma.  The  trabec- 
ulae  (neurokeratin  network,  of  which  some  of  the  larger  strands  would  represent 
the  incisures  of  Schmidt)  would  correspond  to  the  spongioplasm,  and  just  along  the 
outer  side  of  the  axone  would  constitute  the  axolemma.  The  myelin  would  thus 
be  enclosed  within  the  cell  in  much  the  same  manner  as  the  fat  within  the  fat  cell. 

Recent  experiments  of  Bethe  and  others  tend  to  prove  an  interruption  of  the 
perifibrillar  substance  at  the  node  of  Ranvier.  They  consider  the  axone  at  the 
node  as  probably  crossed  by  a  sieve-like  plate,  through  the  holes  of  which  the 
fibrils  pass,  but  which  completely  interrupts  the  perifibrillar  substance.  The 
accuracy  of  these  observations  has  been  disputed. 

Medullated  nerve  fibres  vary  greatly  in  size.  The  finer  fibres 
have  a  diameter  of  from  2  to  4/<,  those  of  medium  size  from  4  to  loii, 
the  largest  from  10  to  20/j.  They  have  few  branches,  and  these  are 
always  given  off  at  the  nodes  of  Ranvier. 

(b)  Medullated  axones  without  a  neurilemma  are  the  medullated 
nerve  fibres  of  the  central  nervous  system  as  described  by  most  observers. 
Cajal,  as  already  mentioned  (p.  120),  describes  these  fibres  as  having 
a  neurilemma.  Their  structure  is  similar  to  the  above-described 
structure  of  a  medullated  nerve  fibre  with  a  neurilemma,  except  for  the 
absence  of  the  latter  sheath. 

As  to  the  physiological  significance  of  the  structural  elements  of  the  neurone,  we 
have  little  absolute  knowledge  but  certain  fairly  well-grounded  theories. 

That  portion  of  the  neurone  which  surrounds  the  nucleus — the  cell  body — is, 
as  already  stated,  the  genetic  centre  of  the  neurone,  the  nucleus  as  in  other  cells  being 
probably  concerned  in  the  general  cell  metabolism.  From  the  behavior  of  the 
processes  when  cut  off  from  the  cell  body  it  is  evident  that  the  latter  is  the  trophic 
or  nutritive  centre  of  the  neurone.  It  seems  probable  that  from  the  standpoint  of 
neurone  activity,  the  cell  body  usually  acts  as  the  functional  centre  of  the  neurone, 
the  processes  acting  mainly  as  channels  through  which  impulses  are  received  and 
distributed.  Certain  facts,  such  for  example  as  the  entire  absence  of  chromophilic 
bodies  in  many  nerve  cells,  which  nevertheless  undoubtedly  functionate;  the  ab- 
sence of  these  bodies  in  all  axones;  the  diminution  of  the  chromatic  substance  dur- 
ing functional  activity;  its  much  greater  diminution  if  activity  be  carried  to  the 
point  of  exhaustion;  these  together  with  its  behavior  under  certain  pathological 
conditions,  all  favor  the  theory  that  the  stainable  substance  of  Nissl  is  not  the  active 
nerve  element  of  the  cell,  but  is  rather  of  the  nature  of  a  nutritive  element. 

There  thus  remains  to  be  considered  as  possible  factors  in  the  transmission  of 
the  nervous  impulse  the  neurofibrils  and  the  perifibrillar  substance.  While  a  few 
investigators  are  inclined  to  magnify  the  importance  of  the  latter,  the  majority 
agree  in  considering  the  neurofibrils  as  the  principal  co)iditcti>ig  mechanism  of  the 
neurone.     The  alreadv  referred  to  observations  of  Bethe  regarding  the  intcrrup- 


122 


THE  TISSUES. 


tion  of  the  perifibrillar  substance  at  the  constricted  portion  of  the  axone  and  at  the 
nodes  of  Ranvier,  thus  making  the  neurofibrils  the  only  continuous  structure,  are 
obviously  in  favor  of  this  view?.  The  neurofibrils  are  probably  a  differentiation 
of  the  spongioplasm,  while  the  perifibrillar  substance  and  chromophilic  bodies  are 
specializations  of  the  hyaloplasm. 

As  to  the  manner  in  which  neurones  are  connected,  there  are  two  main  theories, 
the  contact  theory  and  the  continuity  theory. 


Fig.  73. — A,  B,  C,  Three  cells  of  the  Ventral  Cochlear  Nucleus  of  Rabbit,  showing 
terminals  of  fibres  of  cochlear  nerve  and  their  relations  to  the  cell  bodies  (Cajal).  a, 
a,  a.  Fibres  of  the  cochlear  nerve,  which  break  up  into  terminal  arborizations  upon  the 
cells;  b,  c,  terminal  rings.  The  point  of  contact  between  the  terminals  of  the  one 
neurone  and  the  cell  body  of  the  other  neurone  constitute  a  "  synapsis." 


According  to  the  contact  theory  each  neurone  is  a  distinct  and  separate  entity. 
Association  between  neurones  is  by  contact  or  contiguity  of  the  terminals  of  the 
axone  of  one  neurone  with  the  cell  body  or  dendrites  of  another  neurone,  and  never 
by  continuity  of  their  protoplasm.  This  theory,  which  is  known  as  the  "neurone 
theory"  and  which  received  general  acceptance  as  a  result  of  the  work  of  Golgi, 
His,  Forel,  Cajal,  and  others,  has  been  recently  called  in  question  by  such  promi- 
nent neurologists  as  Apathy,  Bethe,  Held,  and  Nissl,  on  the  ground  that  in  some 
cases  the  neurofibrils  are  continuous  throughout  a  series  of  neurones.  Based  upon 
the  contact  theory  is  the  so-called  "retraction  theory,"  which  held  that  a  neurone 
being  associated  with  other  neurones  only  by  contact  was  able  to  retract  its  terminals, 
thus  breaking  the  association  and  throwing  itself,  as  it  were,  out  of  circuit.     The 


NERVE  TISSUE. 


123 


point  of  contact  between  two  neurones  is  called  a  synapsis  (Fig.  73),  and  the  concep- 
tion that  there  is  some  kind  of  interruption  or  discontinuity  in  neural  circuits  in- 
volving more  than  one  neurone  has  proved  useful  to  physiologists.  It  affords  an 
explanation  of  certain  differences  between  conduction  through  a  circuit  of  two 
or  more  neurones  and  through  a  nerve  fibre.  For  example,  an  impulse  takes  longer 
to  traverse  the  circuit  than  to  traverse  a  nerve  fibre  of  equal  length.  Also  a 
stimulus  may  pass  in  either  direction  along  a  nerve  fibre,  but  cannot  be  "reversed" 
along  a  circuit. 

According  to  the  continuity  theory,  while  the  perifibrillar  substance  is  interrupted 
as  above  described,  the  neurofibrils  are  continuous.  According  to  this  theorv  the 
neurofibrils,  which  form  a  plexus  or  network  within  the  cell  body  and  dendrites, 


Fig.  74. — A,  Normal  Nerve  Fibres  from  Sciatic  Nerv-e  of  Rabbit,  osmic  acid  fixation 
and  stain;  each  fibre  shows  node  of  Ranvier.  B,  Two  fibres  from  distal  part  of  rabbit's 
sciatic  five  days  after  cutting  the  nerve;  shows  segmentation  of  myelin;  C,  three  fibres 
from  distal  part  of  rabbit's  sciatic  three  weeks  after  cutting  nerve;  most  of  the  myelin 
has  been  absorbed  and  onlv  traces  of  the  axones  remain. 


are  connected  with  a  pericellular  network — the  Golgi  net — which  closelv  invests  the 
cell  body  and  its  dendrites.  Externally  the  Golgi  net  is  further  connected  with  the 
neurofibrils  of  the  axones  and  collaterals  of  other  nerve  cells.  This  connection  is 
either  direct,  or,  as  some  believe,  through  another  general  (diffuse)  extracellular 
network.  The  neurofibrils  are  thus,  according  to  this  theory,  continuous  and  form 
two  or  possibly  three  continuous  networks:  (a)  an  intracellular  network,  (b)  a 
pericellular  network  (Golgi),  and  (c)  a  more  diffuse  extracellular  network,  lying 
between  the  cells.  It  seems  probable  that  the  Golgi  network  is  either  non- 
nervous  or  an  artefact.  The  main  point  at  issue  is  whether  the  neurofibrils, 
in  such  pericellular  terminals  as  are  illustrated  in  Fig.  73,  are  continuous  with 
the  neurofibrils  within  the  cell  enveloped  or  are  separate  from  the  latter. 

The  individuality  of  the  neurone  and  the  interdependence  of  its  various  parts 
are  strikingly  shown  by  its  behavior  when  injured.  That  degenerative  changes, 
which  progress  to  complete  disappearance  of  the  nerve  structures,  take  place  in 


124 


THE  TISSUES. 


the  distal  part  of  a  nerve  when  that  nerve  is  cut  across  has  long  been  accepted 
as  one  of  the  fundamental  laws  of  neuropathology  (law  of  Wallerian  degenera- 
tion). In  terms  of  the  neurone  concept  this  would  mean  that  an  axone  cut  off 
from  its  cell  of  origin  degenerates  and  disappears  and  this  behavior  of  the  axone 
would  accord  with  the  already  stated  fact  that  the  cell  body  is  the  trophic  center 
of  the  neurone.  The  degenerative  changes  in  the  axone  are  best  shown  in  their 
earlier  stages  by  an  osmic  acid  (p.  7)  or  by  a  Marchi  (p.  31)  stain.  Later, 
when  the  degenerated  fibres  have  been  largely  replaced  by  connective  tissue,  the 
Weigert  method  is  most  satisfactory,  especially  in  the  central  nervous  system. 


Fig.  75. — Two  Motor  Cells  from  Ventral  Horn  of  Dorsal  Cord  of  Rabbit;  fifteen 
days  after  cutting  major  sacro-sciatic  nerve.  A,  Cell  in  which  the  chromophilic  bodies 
appear  disintegrated  and  nucleus  eccentric;  B,  cell  showing  more  advanced  chromatolysis, 
the  chromophilic  substance  being  present  only  in  the  dendrites  and  around  the  nucleus 
in  the  form  of  a  homogeneous  mass;  nucleus  causes  bulging  of  surface  of  cell. 


The  degeneration  is  not  progressive  from  the  point  of  injury  distal ly,  but  takes 
place  throughout  the  entire  cut  off  portion  at  approximately  the  same  time.  All 
parts  of  the  nerve  fibre  are  affected.  In  the  medullary  sheath  the  changes  con- 
sist in  segmentation  of  the  sheath,  breaking  up  of  the  segments  into  granules  and 
finally  complete  absorption  (Fig.  74).  While  undergoing  these  physical  changes 
chemical  changes  are  also  taking  place  in  the  myelin  which  result  in  its  break- 
ing down  into  simpler  fatty  substances  which  give  the  fat  reaction  to  the  Marchi 
stain.  At  the  same  time  the  neurofibrils  become  irregular  and  granular  and  the 
axis-cylinder  finally  disappears.  The  neurilemma  of  peripheral  nerve  fibres  is 
pjeculiar  in  that  it  does  not  degenerate;  instead  of  this  its  nuclei  proliferate  and 
apparently  play  an  important  role  in  the  disintegration  and  absorption  of  the 
myelin  as  well  as  in  any  regenerative  changes  which  may  occur  later.  The  same 
rule  holds  good   for  dendrites  as  for  axones  as  far  as  it  has  been  possible  to  de- 


NERVE  TISSUE. 


125 


termine,   namely,  that  cut  off  from  their  cells  of  origin  they  undergo  complete 
degeneration. 

At  the  time  the  law  of  Wallerian  degeneration  was  established  it  was  believed 
that  the  central  portion  of  the  nerve  and  the  cell  bodies  remained  intact  after 
division  of  the  nerve.  More  recently  the  method  of  Marchi  (for  nerve  fibres) 
and  the  method  of  Nissl  (for  neurone  bodies)  have  shown  marked  degenerative 
changes  in  the  parts  proximal  to  the  lesion.  The  extent  and  rapidity  of  these 
changes  are  dependent  mainly  upon  two  factors  (i)  the  type  of  neurone — some 
neurones  being  apparently  more  resistant  than  others  to  injury — and  (2)  the 
character  and  location  of  the  injury — e.g.,  pulling  out  the  nerve  causing  the 
greatest   reaction;   cutting  the    nerve,   a   reaction  of  less  intensity;  pinching  the 

A  B 


Fig.  76. — A,  Neuroglia  Cell — Spider  Type — Human  Cerebrum.     B,  Neuroglia  Cell 
— Mossv  Type — Human  Cerebrum. 

nerve,  the  least  degree  of  reaction;  an  injury  near  the  body  of  the  cell  causing 
more  effect  centrally  than  one  near  the  periphery. 

In  the  proximal  stump  of  the  nerve  the  changes  are  similar  to  those  which 
take  place  in  the  distal  stump,  but  these  changes  take  place  more  slowly. 

In  the  cell  body  there  is  an  initial  turgescence,  followed  by  disintegration  and 
disappearance  of  the  chromophilic  bodies  beginning  near  the  center  of  the  cell, 
and  a  displacement  of  the  nucleus  toward  the  periphery.  This  reaction  on  the 
part  of  the  cell  body  to  injury  to  its  axone — "  central  chromatolysis  "  and  "  nuclear 
eccentricity" — is  sufBciently  characteristic  to  have  led  to  the  designation  "  axonal 
degeneration"   (Fig.  75). 

The  importance  of  these  degenerations  from  the  standpoint  of  anatomy  lies  in 
the  fact  that,  combined  with  such  methods  as  Nissl,  Weigert,  and  Marchi,  they 
enable  one  to  trace  the  connections  between  cell  bodies  and  nerve  fibres  through- 
out the  nervous  system. 

Neuroglia. 

This  is  a  peculiar  form  of  connective  tissue  found  only  in  the 
central  nervous  system.  Unlike  the  other  connective  tissues,  neu- 
roglia is  of  ectodermic  origin,  being  developed  from  the  ectodermic 
cells  which   line   the   embrvonic   neural   canal.     These   cells,   at   first 


126 


THE  TISSUES. 


morphologically  identical,  soon  differentiate  into  neuroblasts  or  future 
neurones,  and  spongioblasts  or  future  neuroglia  cells,  the  latter  most 
probably  being  in  the  form  of  a  syncytium.  Later  this  spongioblastic 
syncytium  differentiates  fibres,  the  neuroglia  fibres,  which,  according 
to  Weigert  and  others,  may  be  entirely  separate  from  the  cells 
(Fig.  77).  The  structure  of  neuroglia  would  thus  be  analogous  to 
that  of  fibrous  connective  tissue,  i.e.,  composed  of  cells,  the  neuroglia 
cells,  and  a  fibrillar  intercellular  substance,  the  neuroglia  fibres.  The 
Golgi  method  apparently  reveals  a  great  variety  of  neuroglia  cells  which 
may  be  divided  into  cells  with  straight  radiating  unbranched  processes, 


Fig.  77. — Neuroglia  Cells  and  Fibres  from  the  White  Matter  of  the  Human 
Cerebellum  stained  by  Weigert's  neuroglia  stain.  A,  Neuroglia  cell;  B,  blood-vessel  cut 
longitudinally,  and  C,  blood-vessel  cut  transversely,  showing  enveloping  neuroglia  fibres; 
a,  neuroglia  fibres;  b,  cytoplasm  of  neuroglia  cell.     (Cajal.) 


Spider  cells,  and  rough  thick  branching  cells,  mossy  cells.  It 
seems  probable  that  in  the  former  both  cells  and  fibres  are  stained 
while  in  the  latter  only  portions  of  the  cells  or  syncytium,  this  method 
not  differentiating  between  cells  and  fibres.  Some  authorities  still 
maintain  that  the  fibres  are  to  be  regarded  as  a  part  of  the  cell  in  the 
adult.  The  neuroglia  cells  and  fibres  are  of  marked  pathological 
significance.  Spider  cells  occur  chiefly  in  the  white  matter,  mossy 
cells  in  the  gray  matter  in  connection  with  blood-vessels  (Fig.  76 
A  and  Bj. 


NERVE  TISSUE.  127 


TECHNIC. 


(i)  Pieces  of  the  cerebral  cortex  are  stained  by  one  of  the  Golgi  methods. 
If  the  rapid  or  mixed  silver  method  is  used,  sections  must  be  mounted  in  hard  bal- 
sam without  a  cover;  if  the  slow  silver  or  the  bichloride  method  is  used,  the  sections 
may  be  covered.  Sections  are  cut  from  75  to  ioo,u  in  thickness,  cleared  in  carbol- 
xylol  or  oil  of  origanum  and  mounted  in  balsam.  This  section  shows  only  the  ex- 
ternal morphology  of  the  neurone.  It  is  also  to  be  used  for  studying  the  different 
varieties  of  neuroglia  cells  as  demonstrated  by  Golgi's  method  (see  page  126). 

(2)  Thin  transverse  slices  from  one  of  the  enlargements  of  the  spinal  cord 
are  fixed  in  absolute  alcohol.  Thin  sections  (5  to  10^)  are  stained  by  Nissl's 
method  (page  35)  and  mounted  in  balsam.  This  section  is  for  the  purpose  of 
studying  the  internal  structure  of  the  nerve  cell  and  processes  as  demonstrated  by 
the  method  of  Nissl. 

(3)  Medullated  Nerve  Fibres  (fresh). — Place  a  small  piece  of  one  of  the  sciatic 
or  lumbar  nerves  of  a  recently  killed  frog  in  a  drop  of  salt  solution  and  tease  longi- 
tudinally. Cover  and  examine  as  quickly  as  possible.  Note  the  diameter  of  the 
axone  and  of  the  medullary  sheath  and  the  appearance  of  the  nodes  of  Ranvier. 
An  occasional  neurilemma  nucleus  can  be  distinguished. 

(4)  Medullated  nerve  fibres — fibres  from  the  cauda  equina  (this  material  has 
the  advantage  of  being  comparatively  free  from  fibrous  connective  tissue) — are 
fixed  in  formaHn-Miiller's  fluid  (technic  5,  p.  7),  and  hardened  in  alcohol.  Small 
strands  are  stained  twenty  minutes  in  strong  picro-acid-fuchsin  solution  (technic  2, 
p.  18),  washed  thoroughly  in  strong  alcohol,  cleared  in  oil  of  origanum,  thoroughly 
teased  longitudinally  and  mounted  in  balsam. 

General  References  for  Further  Study  of  Tissues. 

Barker:  The  Nervous  System. 

Bethe:  AUgemeine  Anatomic  und  Physiologie  des  Nervensystem. 
Cabot:  A  Guide  to  the  Clinical  Examination  of  the  Blood  for  Diagnostic  Pur- 
poses. 

Ewing:  Clinical  Pathology  of  the  Blood. 

Hertwig:  Die  Zelle  und  die  Gewebe. 

KoUiker:  Handbuch  der  Gewebelehre. 

Prenant,  Bouin  et  Maillard:  Traite  d'Histologie. 

Ranvier:  Traite  Technique  d'Histologie. 

Van  Gehuchten:  Le  Systeme  nerveux  de  I'homme. 

Wood:  Laboratory  Guide  to  Clinical  Pathology. 


PART  IV. 
THE   ORGANS, 


CHAPTER  I. 

THE  CIRCULATORY  SYSTEM. 

The  circulatory  apparatus  consists  of  two  systems  of  tubular 
structures,  the  blood-vessel  system  and  the  lymph-vessel  system,  which 
serve,  respectively,  for  the  transmission  of  blood  and  lymph. 

THE  BLOOD-VESSEL  SYSTEM. 

This  consists  of  (a)  a  central  propelling  organ,  the  heart;  (b)  a  series 
of  efferent  tubules — the  arteries — which  by  branching  constantly 
increase  in  number  and  decrease  in  calibre,  and  which  serve  to  carry  the 
blood  from  the  heart  to  the  tissues;  (c)  minute  anastomosing  tubules — 
the  capillaries — into  which  the  arteries  empty  and  through  the  walls  of 
which  the  interchange  of  elements  between  the  blood  and  the  other 
tissues  takes  place;  {d)  a  system  of  converging  tubules — the  veins — which 
receive  the  blood  from  the  capillaries,  decrease  in  number  and  increase 
in  size  as  they  approach  the  heart,  and  serve  for  the  return  of  the  blood 
to  that  organ. 

The  entire  system — heart,  arteries,  veins,  capillaries — has  a  com- 
mon and  continuous  lining,  which  consists  of  a  single  layer  of  endothe- 
lial cells.  Of  the  capillaries  this  single  layer  of  cells  forms  the  entire 
wall.  In  the  heart,  arteries,  and  veins,  the  endothelium  serves  simply 
as  the  lining  for  walls  of  muscle  and  connective  tissue. 

Capillaries. 

It  is  convenient  to  describe  these  first  on  account  of  their  simplicity 
of  structure.  A  capillary  is  a  small  vessel  from  7  to  16  ii  in  diameter. 
Its  wall  consists  of  a  single  layer  of  edothelial  cells.  The  cells  are 
somewhat  elongated  in  the  long  axis  of  the  vessel.  Their  edges  are 
serrated  and  are  united  by  a  small  amount  of  intercellular  substance 
(p.  70),  whicli  can  be  demonstrated  by  the  sil\"er  nitrate  stain.  In  cer- 
tain capillaries — those  of  the  early  embryo,  of  the  kidney  glomeruli,  of  the 
chorioid  coat  of  the  eye,  of  the  liver — no  cell  boundaries  can  be  made  out. 
In  these  capillaries  the  endothelium  appears  to  be  of  the  nature  of 
a    syncytium    (p.    62).     Capillaries    branch    without    diminution    in 

131 


132 


THE  ORGANS. 


calibre,  and  these  branches  anastomose  to  form  capillary  networks,  the 
meshes  of  which  differ  in  size  and  shape  in  different  tissues  and  organs 
(Figs.  78,  79,  80).     The  largest  meshed  capillary  networks  are  found  in 


Fig.    78. — ^\''ein  and  Capillaries.     Silver-nitrate  and  ha?matoxylin  stain  (technic  7,  p.  72),  to 
show  outlines  of  endothelial  cells  and  their  nuclei. 

the  serous  membranes  and  in  the  muscles,  while  the  smallest  are 
found  in  the  glands,  as,  e.g.,  the  liver.  As  to  calibre,  the  largest  are 
found  in  the  liver,  the  smallest  in  muscles. 


/  e  d 

Fig.  79. — Diagram  of  Capillaries,  Small  Artery,  and  Vein,  showing  their  structure  and 
relations,  a,  Capillaries;  h,  nuclei  of  capillary  endothelium;  c,  precapillary  arteries;  d, 
arteriole;  c,  small  vein;/,  small  artery. 

In  such  thin  membranous  parts  as  the  web  of  the  frog's  foot,  or  the  wall  of  the 
frog's  bladder,  the  blood  may  be  observed  as  it  flows  through  the  arteries,  capillaries, 
and  veins.  The  current  is  seen  to  be  fastest  in  the  arteries,  and  faster  in  the  center 
of  the  vessel  than  al  its  periphery.     It  is  slower  in  the  veins  and  slowest  in  the  capil- 


THE  CIRCL'LATORY  SYSTEM. 


133 


laries.  In  the  case  of  the  frog's  bladder,  the  mere  exposure  to  the  air  acts  as  a  suffi- 
cient irritant  to  cause  slight  inflammatory  changes,  and  the  leucocytes  maybe  seen 
adhering  to  the  walls  of  the  capillaries  and  passing  through  them  into  the  tissues. 
The  capillary,  both  from  the  thinness  of  its  wall  and  from  the  slowness  with  which 
the  blood  passes  through  it,  is  peculiarly  adapted  for  the  interchange  of  material 
between  the  blood  and  the  tissues,  and  it  is  probable  that  it  is  in  the  capillary  that 
all  such  interchange  takes  place. 

Arteries. 

The  wall  of  an  artery  consists  of  three  coats: 
(i)  An  inner  coat,  the  intima. 

(2)  A  middle  coat,  the  media. 

(3)  An  outer  coat,  the  adventitia. 

The  intima  consists  of  a  single  layer  of  endothelial  cells,  continuous 
with  and  similar  to  that  forming  the  walls  of  the  capillaries,  or,  in  ar- 


FiG.  80. — Capillar)'  Network  from  Human  Pia  Mater,  showing  also  an  arteriole  in 
"optical  section"  and  a  small  vein.  X350.  (Technic  i,  p.  139.)  a,  \'ein;  h,  arteriole; 
c,  large  capillary;  d,  small  capillaries. 

teries  of  considerable  size,  of  this  layer  plus  more  or  less  connective 
tissue.  The  middle  coat  consists  mainly  of  smooth  muscle,  the  outer 
of  connective  tissue. 

The  structure  of  these  three  coats  varies  according  to  the  size  of 
the  artery,  and  while  the  transition  between  them  is  never  abrupt,  it 
is  convenient,  for  purposes  of  description,  to  distinguish  {a)  small 
arteries,  {b)  medium  sized  arteries,  and  (r)  large  arteries. 

Small  Arteries. — Passing  from  a  capillary  to  an  artery,  the  first 


134 


THE  ORGANS. 


change  is  the  addition  of  a  thin  sheath  of  connective  tissue  around 
the  outside  of  the  endothehal  tube.  A  little  farther  back  isolated 
smooth  muscle  cells,  circularly  arranged,  begin  to  appear  between 
the  endothelium  and  the  connective  tissue.  Such  an  artery  is  known 
as  a  precapillary  artery.  The  next  transition  is  the  completion  of 
the  muscular  coat,  the  muscle  cells  now  forming  a  continuous  layer. 
Such  an  artery,  consisting  of  three  distinct  coats,  the  middle  coat 
composed  of  a  single  continuous  layer  of  smooth  muscle  cells,  is  known 
as  an  arteriole  (Fig.  79,  d;  Fig.  80,  h). 


Fig.  81. — From  Cross-section  through  Walls  of  Medium-sized  Artery  and  its  Accom- 
panying Vein.  X75.  (Technic  3,  p.  140.)  A,  Intima  of  artery;  a,  its  endothelial 
layer;  h,  its  intermediary  layer;  c,  its  elastic  layer;  B,  media  of  artery;  C,  adventitia,  the 
upper  part  belonging  to  the  artery,  the  lower  to  the  vein;  within  the  adventitia  are  seen  the 
vasa  vasorum;  D,  media  of  vein;  E,  intima  of  vein;  i,  its  intermediary  layer;  j,  its  endothelial 
layer. 

Medium-sized  Arteries. — This  group  comprises  all  the  named 
arteries  of  the  body  with  the  exception  of  the  aorta  and  the  pulmo- 
nary. Their  walls  arc  formed  of  the  same  three  coats  found  in  the 
arteriole,  but  the  structure  of  these  coats  is  more  elaborate. 

I.  The  INTIMA  consists  of  three  layers  (Fig.  81). 

(a)   An  inner  endothelial  layer  already  described. 

ih)  A  middle  layer,  the  intermediary  layer  of  the  intima.  This 
is  composed  of  delicate  white  and  elastic  fibrils  and  connective-tis- 
sue cells. 


THE  CIRCULATORY  SYSTEM. 


135 


(c)  An  outer  layer,  the  elastic  layer  of  the  intima,  or  memhrana 
elastica  interna — a  thin  fenestrated  membrane  of  elastic  tissue.  This 
membrane  is  intimately  connected  with  the  media  and  marks  the 
boundary  between  the  latter  and  the  intima.  In  the  smallest  of  the 
medium-sized  arteries  the  intermediary  layer  is  often  wanting,  the 
endothelial  cells  resting  directly  upon  the  elastic  membrane.  Owing 
to  the  extensive  amount  of  elastic  tissue  in  their  walls,  there  is  a  post- 


d^--.--: 


Fig.  82. — From  Transverse  Section  of  Dog's  Aorta.      X60.     (Technic  4,  p.  140.)     a,  In- 
tima; h,  media;  c,  adventitia;  d,  vasa  vasorum;  e,  elastic  tissue;/,  endothelium. 


mortem  contraction  of  arteries  which  results  in  the  intima  being  thrown 
up  into  folds.  For  this  reason  the  elastic  membrane  presents,  in 
transverse  sections  of  an  artery,  the  appearance  of  a  wavy  band 
(Fig.  81). 

2.  The  MEDLA.  is  a  thick  coat  of  circularly  disposed  smooth  mus- 
cle cells  (Fig.  81,  5).  Its  thickness  depends  largely  upon  the  size  of 
the  vessel,  though  \-arying  somewhat  for  different  vessels  of  the  same 
size.  A  small  amount  of  fibrillar  connecti\'e  tissue  supports  the 
muscle  cells.     Elastic   tissue  is   present   in   the   media,   the   amount 


136 


THE  ORGANS. 


being  usually  proportionate  to  the  size  of  the  vessel.  In  the  smaller 
of  the  medium-sized  arteries,  the  elastic  tissue  is  disposed  as  delicate 
fibrils  among  the  muscle  cells.  In  larger  arteries  many  coarse  fibres 
are  intermingled  with  the  fine  fibrils.  When  much  elastic  tissue  is 
present  the  muscle  cells  are  separated  into  more  or  less  well-defined 
groups.  In  such  large  arteries  as  the  subclavian  and  the  carotid, 
elastic  tissue  occurs  not  only  as  fibrils  but  also  as  circularly  disposed 
plates  or  fenestrated  membranes. 


ma 


Fig.  83. — From    Transverse   Section   of    Dog's   Aorta,    to   show   Elastic   Tissue.      X6o- 
(Technic  7,  jj.  140.)     Elastic  tissue  stained  black,     a,  Intima;  h,  media;  c,  adventitia. 


3.  The  ADVENTITIA  (Fig.  81,  C)  is  composed  of  loose  fibrous  connec- 
tive tissue  with  some  elastic  fibres.  Occasionally  there  are  scattered 
smooth  muscle  cells.  Both  smooth  muscle  cells  and  elastic  fibres  are 
arranged  longitudinally.  The  adventitia  does  not  form  a  definitely 
outlined  coat  like  the  media  or  intima,  but  blends  externally  with  the 
tissues  surrounding  the  artery  and  serves  to  attach  the  artery  to  these 
tissues.  In  some  of  the  larger  arteries  the  elastic  tissue  of  the  ad- 
ventitia forms  an  especially  well-defined  layer  at  the  outer  margin 


THE  CIRCULATORY  SYSTEM.  137 

of  the  media.  This  is  known  as  the  membrana  elastica  externa.  In 
general,  it  may  be  said  that  the  thickness  of  the  adventitia  and  the 
amount  of  elastic  tissue  present  are  directly  proportionate  to  the  size 
of  the  artery. 

Large  arteries  like  the  aorta  (Fig.  82)  have  the  same  three  coats 
as  small  and  medium-sized  arteries.  The  layers  are  not,  however,  so 
distinct.  This  is  due  mainly  to  the  excessive  amount  of  elastic  tis- 
sue in  the  media  (Fig.  82),  which  makes  indistinct  the  boundaries 
between  intima  and  media,  and  between  media  and  ad^'entitia.  The 
walls  of  the  aorta  are  thin  in  proportion  to  the  size  of  the  vessel,  in- 
creased strength  being  obtained  by  the  decided  increase  in  the  amount 
of  elastic  tissue.  Of  the  intima,  the  endothelial  cells  are  short  and 
polygonal;  the  intermediary  layer  similar  to  that  of  a  medium-sized 
artery;  the  elastic  layer  less  distinct  and  often  broken  up  into  several 
thin  layers.  The  media  consists  mainly  of  elastic  tissue  arranged 
in  circular  plates  or  fenestrated  membranes.  Between  the  elastic- 
tissue  plates  are  groups  of  smooth  muscle  cells  and  some  fibrillated 
connective  tissue.  The  adventitia  resembles  that  of  the  medium-sized 
artery.     There  is  no  external  elastic  membrane. 

Certain  arteries  have  structural  peculiarities.  The  arteries  of  the  brain  and 
cord  are  thin-walled  in  proportion  to  their  calibre,  the  inner  elastic  membrane 
is  especially  well  defined,  and  there  are  few  elastic  fibres  in  the  media.  In  the 
renal,  coeliac,  mesenteric,  and  external  iliac  arteries  there  is  little  or  no  connective 
tissue  separating  the  endothelium  from  the  media.  In  the  subclavian,  the  media 
contains  longitudinal  muscle  cells.  Longitudinally  running  muscle  cells  occur  in 
the  adventitia  of  the  umbilical  arteries,  in  the  iliac,  splenic,  renal,  superior  mesen- 
teric and  dorsalis  penis.  The  radial,  femoral  and  coeliac  arteries  have  compara- 
tively little  elastic  tissue,  while  in  the  common  iliac,  carotid,  and  axillary  the  elastic 
tissue  is  in  excess  of  the  muscular. 

Veins. 

The  walls  of  veins  resemble  those  of  arteries.  There  are  the  same 
three  coats,  intima,  media,  and  adventitia,  and  the  same  elements 
enter  into  the  structure  of  each  coat  (Fig.  81).  \'enous  walls  are  not, 
however,  so  thick  as  those  of  arteries  of  the  same  calibre,  and  the  coats 
arc  not  so  distinctly  differentiated  from  one  another.  The  transition 
from  capillary  through  the  precapillary  vein  to  the  small  \cin  is  similar 
to  that  described  under  arteries  (page  133).  Unlike  the  artery,  the 
thickness  of  the  wall  of  a  vein  and  its  structure  are  not  directly  propor- 
tionate to  the  size  of  the  vessel,  but  depend  also  upon  other  factors  such 


138  THE  ORGANS. 

as  the  position  of  the  vein  and  the  support  given  to  its  walls  by  surround- 
ing structures. 

Of  the  INTIMA  the  endothelial  layer  and  the  intermediary  layer 
are  similar  to  those  of  the  artery.  The  elastic  layer  is  not  always 
present,  is  never  so  distinct,  and  is  not  wavy  as  in  the  artery  (Fig. 
8i).  The  result  is  a  lack  of  demarcation  between  intima  and  media, 
the  connective  tissue  of  the  intermediary  layer  of  the  intima  merging 
with  the  mixed  muscle  and  connective  tissue  of  the  media.  Project- 
ina;  at  intervals  from  the  inner  surface  of  the  wall  of  some  veins  are 
valves.  These  are  derived  entirely  from  intima  and  consist  of  loose 
fibrous  and  elastic  tissue  covered  by  a  single  layer  of  endothelium. 
Valves  are  especially  large  and  strong  in  the  larger  veins  of  the  lower 
limbs.  They  are  absent  in  the  veins  of  the  brain  and  cord  and  their 
membranes,  in  the  veins  of  bones,  in  the  umbilical  vein,  and  in  most  of 
the  \isceral  veins  with  the  exception  of  some  branches  of  the  portal. 

The  MEDIA  of  veins  is  thin  as  compared  with  that  of  arteries  of 
the  same  size.  It  consists  of  fibrous  and  elastic  tissue  and  smooth 
muscle  cells.  The  amount  of  muscle  is  comparatively  small  and  the 
cells  are  arranged  in  groups  through  the  connective  tissue. 

The  ADVENTiTiA  is  well  developed  in  proportion  to  the  media. 
It  consists  of  mixed  fibrous  and  elastic  tissue  and  usually  contains 
along  its  inner  margin  small  bundles  of  longitudinally  disposed  smooth 
muscle  cells. 

The  media  is  thickest  in  the  veins  of  the  lower  extremities  and 
in  the  veins  of  the  skin.  In  the  veins  of  the  head  and  abdomen  the 
media  is  very  thin,  while  in  the  subclavian  and  superior  vena  cava 
and  in  the  veins  of  bones,  of  the  pia  mater,  dura  mater,  and  retina, 
there  is  an  almost  entire  absence  of  media. 

Arteries  are  as  a  rule  empty  after  death,  while  veins  contain  blood. 
The  absence  of  much  elastic  tissue  in  the  walls  of  the  veins  prevents 
any  such  extensive  post-mortem  contraction  as  occurs  in  the  arteries. 
Veins  tend  to  collapse  after  death,  but  are  usually  prevented  from 
doing  so  by  the  presence  of  blood  in  them. 

In  the  iliac  and  femoral  veins,  longitudinally  disposed  muscle  occurs  in  the  inner 
part  of  the  media.  The  umbilical  vein,  like  the  corresponding  artery,  has  three 
distinct  muscular  coats.  Longitudinal  muscle  fibres  are  present  in  the  adventitia 
of  the  superior  vena  cava  (hepatic  and  abdominal  portion)  and  of  the  portal  and 
hepatic  veins.  In  the  upper  portion  of  the  inferior  vena  cava,  in  the  superior  vena 
cava,  the  jugular,  innominate,  and  subclavian,  there  is  little  muscle  tissue  in  any  of 
the  coats,  while  in  the  veins  of  the  brain  and  its  membranes,  the  retina,  the  placenta 
and  the  bones,  no  muscle  is  present. 


THE  CIRCULATORY  SYSTEM.  139 

Vasa  Vasorum. — Medium  and  large  arteries  and  veins  are  supplied 
with  small  nutrient  vessels — vasa  vasorum.  These  vessels  run  in  the 
ad\'entitia,  small  branches  penetrating  the  media  (Figs.  8i  and  82). 

Lymph  channels  are  found  on  the  outer  surface  of  many  blood- 
vessels. Some  of  the  smaller  vessels  are  surrounded  by  spaces  lined  by 
endothelium — perivascular  lymph  spaces.  These  communicate  with 
the  general  lymphatic  system. 

Nerves. — The  walls  of  the  blood-vessels  are  supplied  with  both 
medullated  and  non-medullated  fibres.  The  latter  are  axones  of 
sympathetic  neurones.  As  these  nerves  control  the  calibre  of  the 
vessels  they  are  known  as  vasomotor  nerves.  They  form  plexuses 
in  the  adventitia,  from  which  are  given  off  branches  which  pene- 
trate the  media  and  terminate  on  the  muscle  cells.  The  medul- 
lated fibres  are  the  peripheral  arms  of  spinal  or  cranial  ganglion  cells. 
The  larger  fibres  run  in  the  connective  tissue  outside  the  adventitia. 
From  these  are  given  off  branches  which  enter  the  media,  divide  re- 
peatedly, lose  their  medullary  sheaths,  and  terminate  mainly  in  the 
media,  although  some  fibres  have  been  traced  to  their  terminations  in 
the  intima. 

TECHNIC. 

(i)  Capillaries,  Arterioles,  Small  Arteries,  and  Veins. — Fix  an  entire  brain,  or 
slices  about  an  inch  thick  from  its  surface,  in  formalin-Muller's  fluid  for  twenty- 
four  hours  (technic  5,  p.  7).  Remove  the  pia  mater,  especially  the  thinner  parts 
which  lie  in  the  sulci  between  the  convolutions,  and  harden  in  graded  alcohols. 
Select  a  thin  piece,  stain  with  hsematoxylin  (lightly)  and  eosin  (strongly)  (technic 
I,  p.  18),  and  mount  in  balsam  or  in  eosin-glycerin.  The  veins,  having  thin  walls 
and  being  usually  well  filled  with  blood,  appear  distinct  and  red  from  the  eosin- 
stained  red  cells.  The  arteries,  having  thicker  walls,  in  which  are  many  haemo- 
globin-stained nuclei,  have  a  rather  purple  color.  Between  the  larger  vessels  can 
be  seen  a  network  of  anastomosing  capillaries  with  their  thin  walls  and  bulging 
nuclei.  Some  are  filled  with  blood  cells;  others  are  empty  with  their  collapsed 
walls  in  apposition.  Note  the  appearance  of  an  arteriole,  first  focusing  on  its 
upper  surface,  then  focusing  down  through  the  vessel.  In  this  way  what  is  known 
as  an  "optical  section"  is  obtained,  the  artery  appearing  as  if  cut  longitudinally. 
Trace  the  transition  from  arteriole  to  precapillary  artery  and  the  breaking  up  of  the 
latter  into  the  capillary  network.  Similarly  follow  the  convergence  of  capillaries 
to  form  a  small  vein. 

(2)  Instructive  pictures  of  the  relations  of  arteries,  capillaries,  and  veins  in  liv- 
ing tissues  may  be  obtained  by  curarizing  a  frog,  distending  the  bladder  with  nor- 
mal saline  introduced  through  a  small  catheter  or  cannula,  opening  the  abdomen 
and  drawing  out  the  bladder,  which  can  then  be  arranged  upon  the  stage  of  the 
microscope.  The  passage  of  the  blood  from  the  arteries  through  the  capillary  net- 
work and  into  the  veins  is  beautifully  demonstrated. 


140  THE  ORGANS. 

(3)  For  studying  the  structure  of  the  walls  of  a  medium-sized  artery  and  vein 
remove  a  portion  of  the  radial  artery,  or  other  artery  of  similar  size,  and  its  accom- 
panying vein,  together  with  some  of  the  surrounding  tissues.  Suspend  the  vessels, 
with  a  small  weight  attached,  in  formaUn-Miiller's  fluid  (technic  5,  p.  7).  Sec- 
tions should  be  cut  transversely,  stained  with  haematoxylin-eosin  (technic  i,  p.  18), 
or  with  haematoxylin-picro-acid  fuchsin  (technic  3,  p.  19),  and  mounted  in  balsam. 
The  vessels  of  the  adventitia — vasa  vasorum — are  convenient  for  studying  the 
structure  of  arterioles  and  small  veins. 

(4)  Fix  a  piece  of  aorta  in  formalin-Miiller's  fluid,  care  being  taken  not  to 
touch  the  delicate  endothelial  lining.  Stain  transverse  sections  with  hasmatoxylin- 
eosin  or  with  h£ematoxylin-picro-acid  fuchsin  and  mount  in  balsam. 

(5)  The  outlines  of  the  lining  endothelial  cells  may  be  demonstrated  as  follows: 
Kill  a  small  animal,  cut  the  aorta,  insert  a  glass  cannula  and,  under  low  pressure, 
thoroughly  wash  out  the  entire  vascular  system  with  distilled  water.  Follow  the 
water  by  a  one-per-cent.  aqueous  solution  of  silver  nitrate.  Remove  some  of  the 
smaller  vessels,  split  longitudinally,  mount  in  glycerine,  and  expose  to  the  direct 
sunlight.  After  the  specimen  has  turned  brown  examine  with  the  low  power.  The 
outlines  of  the  cells  should  appear  brown  or  black. 

(6)  The  endothelium  of  the  smaller  vessels  and  capillaries  may  also  be  demon- 
strated in  the  specimen  described  under  technic  8,  p.  72. 

(7)  The  elastic  tissue  of  the  blood-vessels  is  best  demonstrated  by  means  of 
Weigert's  elastic-tissue  stain.  Prepare  sections  of  medium-sized  vessels  and  of 
the  aorta,  as  above  described  (3),  and  stain  as  in  technic  3,  p.  26. 

The  Heart. 

The  heart  is  a  part  of  the  blood-vessel  system  especially  differ- 
entiated for  the  purpose  of  propelling  the  blood  through  the  vessels. 

The  main  mass  of  the  heart  wall  consists  of  a  special  form  of 
muscle  tissue  already  described  as  heart  muscle  (page  106).  This 
constitutes  the  myocardium.  On  its  inner  and  outer  sides  the  myo- 
cardium is  covered  by  connective-tissue  membranes  lined,  respectively, 
with  endothelium  and  mesothelium  and  known  as  the  endocardium 
and  epicardium. 

The  MYOCARDIUM  varies  in  thickness  in  different  parts  of  the 
heart,  being  thickest  in  the  left  ventricle,  thinnest  in  the  auricles. 
A  ring  of  dense  connective  tissue,  the  auriculo-ventricular  ring,  com- 
pletely separates  the  muscle  of  the  auricles  from  that  of  the  ven- 
tricles. The  auricular  muscle  consists  of  an  outer  coat  common  to 
both  auricles,  the  fibres  of  which  have  a  transverse  direction,  and  of 
an  inner  coat,  independent  for  each  auricle,  the  fibres  of  which  are 
longitudinally  disposed.  Between  the  two  coats  bundles  of  muscle 
fibres  are  frequently  found  which  run  in  various  directions. 

The  disposition  of  the  muscle  tissue  of  the  ventricles  is  much 


THE  CIRCULATORY  SYSTEM.  141 

more  complicated.  It  is  usually  described  as  composed  of  several 
layers,  the  fibres  of  which  run  in  different  directions.  The  meaning 
of  these  fibre  layers  becomes  apparent  when  we  study  the  arrange- 
ment of  the  fibres  in  embryonic  hearts  in  which  the  connective  tissue 
has  been  broken  down  by  maceration.  Thus  dissected,  the  muscle  of 
the  ventricles  is  seen  to  consist  mainly  of  two  sets  of  fibres,  a  super- 
ficial set  and  a  deep  set.  These  run  at  right  angles  to  each  other. 
Both  sets  of  fibres  begin  at  the  auriculo-ventricular  rings.  The 
superficial  fibres  wind  around  both  ventricles  in  a  spiral  manner,  be- 
coming constantly  deeper,  to  terminate  in  the  papillary  muscles  of  the 
opposite  ventricle.  The  deeper  fibres  pass  from  the  auriculo-ven- 
tricular ring  around  the  ventricle  of  the  same  side,  through  the  inter- 
ventricular septum  and  terminate  in  the  papillary  muscles  of  the 
opposite  ventricle. 

The  ENDOCARDIUM  covcrs  the  inner  surface  of  the  myocardium 
and  forms  the  serous  lining  of  all  the  chambers  of  the  heart.  At  the 
arterial  and  venous  orifices  it  is  seen  to  be  continuous  with  and  simi- 
lar in  structure  to  the  intima  of  the  vessels.  It  consists  of  two  lay- 
ers: {a)  an  inner  composed  of  a  single  layer  of  endothelial  cells,  cor- 
responding to  the  endothelial  lining  of  the  blood-vessels;  and  {h) 
an  outer  composed  of  mixed  fibrous  and  elastic  tissue  and  smooth 
muscle  cells.  Externally  the  endocardium  is  closely  attached  to  the 
myocardium. 

Strong  fibrous  rings  (annul i  fibrosi),  composed  of  mixed  fibrous 
and  elastic  tissue,  surround  the  openings  between  auricles  and  ven- 
tricles.  Similar  but  more  delicate  rings  encircle  the  openings  from 
the  heart  into  the  blood-vessels. 

The  heart  valves  are  attached  at  their  bases  to  the  annuli  fibrosi. 
They  are  folds  of  the  endocardium,  and  like  the  latter  consist  of  fibrous 
and  elastic  tissue  continuous  with  that  of  the  rings  and  covered  by 
a  layer  of  endothelium. 

The  EPICARDIUM  is  the  visceral  layer  of  the  pericardium.  It  is  a 
serous  membrane  like  the  endocardium,  which  it  resembles  in  struc- 
ture. It  consists  of  a  layer  of  mixed  fibrous  and  elastic  tissue  cov- 
ered over  by  a  single  layer  of  mesothelial  cells.  Beneath  the  epicar- 
dium  there  is  usually  more  or  less  fat. 

Blood-vessels. — Blood  for  the  nutrition  of  the  heart  is  supplied 
through  the  coronary  arteries.  The  larger  branches  run  in  the  con- 
nective tissue  which  separates  the  bundles  of  muscle  fibres.  From 
these,  smaller  l)ranches  pass  in  among  the  indi\idual  fibres,  where 


142  THE  ORGANS. 

they  break  up  into  a  rich  capillary  network  with  elongated  meshes. 
From  the  myocardium,  capillaries  penetrate  the  connective  tissue  of 
the  epicardium  and  endocardium.  The  auriculo-ventricular  valves 
are  supplied  with  blood-vessels,  while  in  the  semilunar  valves  blood- 
vessels are  wanting. 

Lymphatics. — Lymph  channels  traverse  the  epicardium  and  endo- 
cardium and  enter  the  valves.  Within  the  myocardium  minute 
lymph  vessels  have  been  demonstrated  between  the  muscle  fibres  and 
accompanying  the  blood-vessels. 

Nerves. — These  are  derived  from  both  cerebro-spinal  and  sym- 
pathetic systems,  and  consist  of  both  medullated  and  non-medullated 
fibres.  Sympathetic  ganglion  cells  are  distributed  in  groups  through- 
out the  myocardium.  Among  these  cells  the  nerve  fibres  form  plex- 
uses from  which  both  motor  and  sensory  terminals  are  given  off  to 
the  muscle.     (For  nerve  endings  in  heart  muscle  see  page  393.) 

TECHNIC. 

(i)  The  Heart. — Cut  pieces  through  the  entire  thickness  of  the  "wall  of  one  of 
the  ventricles,  care  being  talcen  not  to  touch  either  the  serous  surface  or  the  lining 
endothelium.  Fix  in  formaUn-MiJller's  fluid  (technic  5,  p.  7).  Cut  transverse 
and  longitudinal  sections;  stain  with  hasmatoxylin-eosin  (technic  i,  p.  18)  and 
mount  in  balsam. 

(2)  Treat  the  entire  heart  of  a  small  animal  {e.g.,  guinea-pig  or  frog)  in  the 
same  manner  as  the  preceding,  making  transverse  sections  through  both  ventricles. 

(3)  An  entire  heart,  human  or  animal,  may  be  fixed  in  the  distended  condition 
by  filling  with  formahn-Miiller's  fluid  under  low  pressure  and  then  tying  off  the 
vessels.  The  entire  heart  thus  distended  is  placed  in  a  large  quantity  of  the  same 
fixative. 

Development  of  the  Circulatory  System. 

The  blood-vessels  and  the  heart  begin  their  development  separately 
and  afterward  become  united.  Both  arc  derived  from  mesoderm. 
The  earliest  vessels  to  be  formed  are  the  capillaries.  These  make  their 
appearance  in  the  mcsodermic  tissue  near  the  periphery  of  the  area 
vasculosa  which  surrounds  the  developing  emljryo.  Here  groups 
of  cells  known  as  "blood  islands^'  differentiate  from  the  rest  of  the 
mesodermic  cells.  The  superficial  cells  of  these  islands  become  flat- 
tened to  form  the  endothelium,  while  the  remaining  cells  form  the 
erythroblasts.  These  represent  the  earliest  blood-vessels.  These  chan- 
nels, which  are  at  first  unconnected,  anastomose  and  give  rise  to  a  net- 


THE  CIRCULATORY  SYSTEM.  143 

work  of  channels  which  are  the  earliest  capillaries.  In  regard  to  the 
origin  of  the  later  vessels  in  the  extraembryonic  area,  and  those  within 
the  embryo,  there  are  two  views :  (i)  that  they  represent  outgrowths  from 
the  original  capillaries;  (2)  that  they  arise  in  situ  in  the  same  manner 
as  the  earliest  capillaries  and  unite  secondarily  to  form  networks.  The 
weight  of  evidence  at  present  favors  the  latter  view.  The  entire  vascu- 
lar system  is  at  first  represented  by  a  network  of  capillaries.  As  develop- 
ment proceeds  some  of  the  channels  enlarge  to  form  the  arteries  and 
veins,  the  smooth  muscle  and  connective  tissue  of  the  walls  being 
differentiated  from  the  surrounding  mesoderm. 

The  heart  first  appears  as  an  endothelial  tube,  the  primitive 
endocardium,  at  a  very  early  age  of  embryonic  life.  The  origin  of 
the  cardiac  endothelium  is  not  definitely  known.  It  is  believed  by 
some  to  be  of  entodermic  origin,  by  others  of  mesodermic,  by  still 
others  to  be  partly  derived  from  each  of  these  layers.  Around  this 
endothelial  tube,  but  separated  from  it  by  a  space,  there  develops 
from  mesoderm  an  entirely  distinct  muscular  tube,  the  primitive 
myocardium.  These  two  tubes  are  at  first  united  only  in  places  by  bands 
of  connective  tissue.  Later  they  unite  so  that  the  inner  tube,  the 
endocardium,  becomes  a  lining  for  the  outer  tube,  the  myocardium. 
The  union  of  the  two  heart  tubes  occurs  very  early.  In  the  human 
embryo  of  2  to  3  mm.  the  heart  is  a  single,  slightly  coiled  tube  con- 
nected at  its  cephalic  end  with  the  ventral  aorta  and  caudally  with 
the  omphalo-mesenteric  veins.  The  epicardium,  as  the  visceral  layer 
of  the  pericardium,  has  a  separate  origin,  being  constricted  off  from 
that  portion  of  the  mesoderm  which  lines  the  primary  body  cavity. 

THE  LYMPH-VESSEL  SYSTEM. 

The  larger  lymph  vessels  are  similar  in  structure  to  veins.  Their 
walls  are,  however,  thinner  than  those  of  veins  of  the  same  calibre 
and  they  contain  more  valves.  They  are  capable  of  great  distention, 
and  when  empty  collapse  so  that  their  thin  walls  are  in  apposition. 

The  largest  of  the  lymph  vessels,  the  thoracic  duct,  has  three  well- 
defined  coats:  an  intima  consisting  of  the  usual  lining  endothelium 
resting  upon  a  subendothelial  layer  of  delicate  fibro-elastic  tissue,  the 
outermost  elastic  fibres  having  a  longitudinal  arrangement;  a  fairly 
thick  media  of  circularly  disposed  smooth  muscle  cells;  and  an  ad- 
ventilia  which  is  strengthened  I)y  Inmdles  of  longitudinal  smooth 
muscle. 


144 


THE  ORGANS. 


Lymph  capillaries  resemble  blood  capillaries  in  that  their  walls 
are  composed  of  a  single  layer  of  endothelial  cells.  The  cells  are 
rather  larger  and  more  irregular  than  in  blood  capillaries,  the  capil- 
laries themselves  are  larger,  and,  instead  of  being  of  uniform  diameter 
throughout,  vary  greatly  in  calibre  within  short  distances.  In  certain 
tissues  dense  networks  of  these  lymph  capillaries  are  found.  Cleft-like 
lymph  spaces — perivascular  lymph  spaces — partially  surround  the 
walls  of  the  smaller  blood-vessels. 

Lymph  spaces  without  endothelial  or  other  apparent  lining  also  occur. 
Examples  of  these  are  the  pericellular  lymph  spaces  found  in  various 
tissues  and  the  canal iculi  of  the  cornea  and  of  bone  (pages  74  and  93). 


Septum. 


Trabecula  of 
cells  in  cross- 
section. 

Distended 
blood  capil- 
laries. 


Efferent  vein. 


Fig.  84. — Section  of  human  carotid  gland.      X  ]6o.     (Schaper.) 

Similar  in  character  to  lymph  spaces  are  the  body  cavities,  peri- 
toneal, pleural,  and  pericardial,  with  their  linings  of  serous  membranes. 
These  cavities  first  appear  in  the  embryo  as  a  cleft  in  the  mesoderm 
■ — the  ca'lom,  body  cavity,  or  pleiiro peritoneal  cleft.  This  cleft  is  lined 
with  mesothelium  beneath  which  the  stroma  is  formed.  These  mem- 
branes not  only  line  the  cavities,  but  are  reflected  over  most  of  the 
viscera  of  the  abdomen  and  thorax.  They  consist  of  a  stroma  of 
mixed  fibrous  and  elastic  tissue,  covered  on  its  inner  side  by  a  layer 
of  mesothelium,  the  two  being  separated  by  a  homogeneous  basement 
meml.)rane.  The  stroma  contains  numerous  lymphatics.  These  have 
been  described  as  communicating  with  the  free  surfaces  by  means  of 


THE  CIRCULATORY  SYSTEM. 


145 


openings — stomata.  Recent  observations,  however,  would  seem  to 
indicate  that  these  stomata  are  artefacts. 

That  the  lymph-vessels  form  a  definite  and  closed  system  of  channels 
and  are  not  in  direct  communication  with  the  lymph  spaces  has  been 
clearly  demonstrated. 

The  lymphatics  apparently  originate  from  the  vascular  system, 
starting  as  four  buds,  two  from  the  veins  of  the  neck,  and  two' from 
veins  in  the  inguinal  redon. 


M 


«^^  ..- 


,-,'^— «»>   .^•., 


iS^' 


Fig.  85. — Section  through  coccygeal  gland   (Walker),     i.  Blood  space;   2.  epithe- 
lium;   3.  connective  tissue. 


TECHNIC. 


(i)  Remove  a  portion  of  the  central  tendon  of  a  rabbit's  diaphragm.  Rub 
the  pleural  surface  gently  with  the  finger  or  with  a  brush  to  remove  the  mesothe- 
lium.  Rinse  in  distilled  water  and  treat  with  silver  nitrate  as  in  technic  7,  p.  72. 
Mount  in  glycerin.  If  the  silver  impregnation  is  successful,  the  networks  of  coarser 
and  finer  lymphatics  can  be  seen  as  well  as  the  outlines  of  the  endothelium  of  their 
walls.  If  care  has  been  taken  not  to  touch  the  peritoneal  surface,  the  peritoneal 
mesothelium  and  the  stomata  are  frequently  seen. 

(2)  The  Thoracic  Duct. — Remove  a  portion  of  the  thoracic  duct,  fi.x  in  forma- 
lin-Miiller's  fluid  (technic  5,  p.  7),  and  stain  sections  with  h;cmato.\ylin-eosin 
(technic  i,  p.  18). 


146  the  organs. 

The  Carotid  Gland. 

This  is  a  small  ductless  gland,  about  the  size  of  a  rice  grain,  which 
lies  at  the  bifurcation  of  the  carotid  artery.  It  is  composed  of  a  vascu- 
lar connective  tissue  supporting  spheroidal  groups  of  polyhedral  epithe- 
lial cells  which  are  closely  associated  with  tufts  of  capillaries.  Some  of 
the  gland  cells  take  a  brownish  stain  with  chromic  acid  similar  to  the 
medullary  cells  of  the  adrenal  (Fig.  84). 

The  Coccygeal  Gland. 

This  is  also  a  ductless  gland  similar  in  structure  to  the  preceding, 
but  with  much  more  irregularly  arranged  groups  of  cells.  According 
to  some  observers,  the  cells  of  the  coccygeal  gland  differ  from  those  of 
the  carotid  in  that  they  do  not  give  the  chromaffin  reaction,  the  gland 
conforming  more  to  the  structure  of  lymphoid  tissue  (Fig.  85). 

TECHNIC. 

Technic  same  as  for  Thyreoid  Gland,  page  285. 

General  References  for  Further  Study  of  the  Circulatory  System. 

Kolliker:  Handbuch  der  Gewebelehre  des  Menschen,  vol.  iii. 
Stohr:  Text-book  of  Histology. 

Schafer:  Histology  and  Microscopic  Anatomy,  in  Quain's  Elements  of  Anat- 
omy, tenth  edition. 


CHAPTER  IT. 
LYMPHATIC  ORGANS. 

The  Lymph  Nodes. 

Lymph  nodes  are  small  bodies,  usually  oval  or  bean-shaped,  which 
are  distributed  along  the  course  of  the  lymph  vessels.  In  some  regions 
Ihey  are  arranged  in  series  forming  "chains"  of  lymph  nodes  as, 
e.g.,  the  axillary  and  inguinal. 

Each  lymph  node  is  surrounded  by  a  capsule  of  connective  tissue 
which  sends  trabeciilce  or  septa  into  the  organ.     The  capsule  and  septa 


■A}!^-_^^         ?^A/:'^ 


h  g  f 

Fig.  86. — Section  through  Entire  Human  Lymph  Node,  including  Hilum.  X15. 
(Technic  i,  p.  150.)  Dark  zone,  corte.x;  hght  central  area,  medulla,  a,  Lymph  nodule  of 
cortex;  /),  germinal  centres;  c,  trabecule  containing  blood-vessels;  d,  capsule;  e,  hilum; 
/,  lymph  sinus  of  medulla;  g,  lymph  cords  of  medulla;  h,  lymph  sinuses  of  medulla  and 
cortex. 

constitute  the  connective-tissue  framework  of  the  node,  and  serve  as  a 
support  for  the  lymphatic  tissue  (Fig.  86). 

The  capsule  is  composed  of  fibrous  connective  tissue  arranged  in 
two  layers.     In  the  outer,  the  fibres  are  loosely  arranged  and  serve, 

147 


14S  THE  ORGANS. 

like  the  fibres  of  the  arterial  adventitia,  to  attach  the  node  to  the 
surrounding  tissues.  The  inner  layer  of  the  capsule  consists  of  a 
more  dense  connective  tissue  and  contains  some  smooth  muscle  cells. 
At  one  point,  known  as  the  hilum  (Fig.  86),  there  is  a  depression 
where  the  connective  tissue  of  the  capsule  extends  deep  into  the  sub- 
stance of  the  node.  This  serves  as  the  point  of  entrance  for  the  main 
arteries  and  nerves,  and  of  exit  for  the  veins  and  efferent  lymph  vessels. 

The  connective-tissue  septa,  which  extend  from  the  capsule  into 
the  interior  of  the  node  incompletely  di\'ide  it  into  irregular  inter- 
communicating compartments.  In  the  peripheral  portion  of  the  node 
these  compartments  are  somewhat  spheroidal  or  pear-shaped.  Toward 
the  centre  of  the  node  the  septa  branch  and  anastomose  freely,  with  the 
result  that  the  compartments  are  here  narrower,  more  irregular,  and 
less  well  defined.  This  arrangement  of  the  connective  tissue  allows 
the  division  of  the  node  into  two  parts,  an  outer  peripheral  part  or 
cortex  and  a  central  portion,  the  medulla  (Fig.  86). 

Within  the  compartments  formed  by  the  capsule  and  the  septa  is 
the  lymphatic  tissue  (for  structure  see  page  84).  In  the  cortex  where 
the  compartments  are  large  and  spheroidal  or  pear-shaped,  the  lymph- 
atic tissue  is  of  the  compact  variety,  and  is  arranged  in  masses 
which  correspond  in  shape  to  the  compartments.  These  are  known 
as  lymph  nodules  (Fig.  86).  In  the  centre  of  each  nodule  is  usually 
an  area  in  which  the  cells  are  larger,  are  not  so  closely  packed,  and 
show  marked  mitosis.  As  it  is  here  that  active  proliferation  of  lymph- 
oid cells  takes  place,  this  area  is  known  as  the  germinal  centre  (Figs. 
86  and  87).  Immediately  surrounding  the  germinal  centre  is  a  zone 
in  which  the  lymphoid  cells  are  more  closely  packed  than  elsewhere 
in  the  nodule  (Fig.  87).  This  is  apparently  due  to  the  active  pro- 
duction of  new  cells  at  the  germinal  centre  and  the  consequent  pushing 
outward  of  the  surrounding  cells.  In  stained  sections  the  centre  of 
the  nodule  is  thus  lightly  stained,  while  immediately  surrounding 
this  light  area  is  the  darkest  portion  of  the  nodule  (Fig.  87).  From 
the  inner  sides  of  the  nodules  strands  of  lymphoid  tissue  extend  into 
the  medulla.  These  are  known  as  lymph  cords,  and  anastomose 
freely  in  the  small  irregular  compartments  of  the  medulla.  In  both 
cortex  and  medulla  the  lymphoid  tissue  is  always  separated  from  the 
capsule  or  from  the  septa  by  a  distinct  space — the  lymph  sinus — 
which  is  bridged  over  by  reticular  tissue  containing  comparatively 
few  lymphoid  cells  (Fig.  87).  These  sinuses  form  a  continuous  system 
of  anastomosin"  channels  throughout  the  node. 


LYMPHATIC  ORGANS. 


149 


The  reticular  connective  tissue  (page  d>T)),  which  forms  a  part  of 
the  lymphatic  tissue  proper,  is  continuous  with  the  fibrous  connec- 
tive-tissue framework  of  the  organ  in  such  a  manner  that  it  is  im- 
possible to  determine  any  demarcation  between  the  two  tissues.  In 
the  lymph  nodules,  and  wherever  the  lymphoid  cells  are  densely 
packed,  the  underlying  reticular  network  is  almost  completely  obscured. 
Crossing  the  sinuses,  especially  those  of  the  medulla,  and  in  specimens 


Fig.  87. — Section  through  Cortex  and  Portion  of  Medulla  of  Human  Lymph  Node. 
(Technic  2,  p.  150.)  a,  Capsule;  b,  lymph  sinus;  c,  trabecula;  d,  closely  packed  cells  at 
outer  border  of  lymph  nodule;  e,  germinal  centre;  /,  lymph  cords  in  medulla. 


in  which  the  cells  have  been  largely  washed  out  or  removed  by  macera- 
tion, the  reticular  structure  is  well  shown. 

The  lymphoid  tissue  proper,  as  represented  by  the  lymph  nodules 
and  anastomosing  lymph  cords,  is  thus,  as  it  were,  suspended  in  the 
meshes  of  a  reticulum  which  is  swung  from  the  capsule  and  trabec- 
ulae.  As  both  nodules  and  cords  are  everywhere  separated  from  cap- 
sule and  trabeculse  by  the  sinuses,  and  as  these  latter  serve  for  the 
passage  of  lymph  through  the  node,  it  is  seen  that  the  lymphatic  tis- 
sue of  the  node  is  broken  up  in  such  a  manner  as  to  be  bathed  on 
all  sides  by  the  circulating  lymph. 

In  addition  to  the  definitely  formed  lymph  nodes  and  the  well- 
defined  collections  of  lymph  nodules,  such  as  those  of  the  tonsil  or 
of  Peyer's  patches,  small  nodules  or  groups  of  lymphoid  cells  have  a 
wide  distribution  throughout  the  various  organs.  While  many  of 
these  collections  of  lymphatic  tissue  are  inconspicuous,  still  the  ag- 
gregate of  lymph  tissue  thus  distributed  is  by  no  means  inconsider- 


150  THE  ORGANS. 

able.  The  most  important  will  be  described  in  connection  with  the 
organs  in  which  they  occur. 

Blood-vessels. — Those  which  enter  the  hilum  carry  the  main 
blood  supply  to  the  organ.  Most  of  the  arteries  pass  directly  into  the 
lymphatic  tissue,  where  they  break  up  into  dense  capillary  networks. 
Some  of  the  arteries,  instead  of  passing  directly  to  the  lymphatic  tissue, 
follow  the  septa,  supplying  these  and  the  capsule,  and  also  sending 
branches  to  the  surrounding  lymphatic  tissue.  A  few  small  vessels 
enter  the  capsule  along  the  convexity  of  the  organ  and  are  distributed 
to  the  capsule  and  to  the  larger  septa. 

Lymphatics. — The  afferent  lymph  vessels  enter  the  node  on  its 
convex  surface  opposite  the  hilum,  penetrate  the  capsule,  and  pour 
their  lymph  into  the  cortical  sinuses.  The  lymph  passes  through  the 
sinuses  of  both  cortex  and  medulla,  and  is  collected  by  the  efferent 
lymph  vessels  which  leave  the  organ  at  the  hilum.  Within  the  node 
the  lymph  comes  in  contact  with  the  superficial  cells  of  the  nodules 
and  of  the  lymph  cords.  These  cells  are  constantly  passing  out  into 
the  lymph  stream  so  that  the  lymph  leaves  the  node  much  richer  in 
cellular  elements. 

Nerves  are  not  abundant.  Both  medullated  and  non-medullated 
fibres  occur.     Their  exact  modes  of  termination  are  not  known. 

TECHNIC. 

(i)  Remove  several  lymph  nodes  from  one  of  the  lower  animals  (ox,  cat,  dog. 
rabbit),  fix  in  formalin-Miiller's  fluid  (technic  5,  p.  7),  and  harden  in  alcohol,. 
Cut  thin  sections  through  the  hilum,  stain  with  haematoxylin-eosin  (technic  i,  p. 
18),  or  with  haematoxylin-picro-acid-fuchsin  (technic  3,  p.  19),  and  mount  in  balsam. 

(2)  Expose  a  chain  of  lymph  nodules  {e.g.,  the  cervical  or  inguinal  of  a  recently 
killed  dog  or  cat).  Insert  a  small  cannula  or  needle  into  the  uppermost  node 
and  inject  formalin-Miiller's  fluid  until  the  node  becomes  tense.  By  now  slightly 
increasing  the  pressure  the  fluid  may  be  made  to  pass  into  the  second  node,  and 
so  through  the  entire  chain.  The  nodes  are  then  carefully  dissected  out  and 
placed  for  twenty-four  hours  in  formalin-Miiller's  fluid,  then  hardened  in  alcohoL 
Sections  are  cut  through  the  hilum,  stained  with  haimatoxylin-eosin  or  with  hsema- 
toxylin-picro-acid-fuchsin  and  mounted  in  balsam.  Near  the  centre  of  the  chain 
arc  usually  found  nodes  in  which  the  lymph  sinuses  are  properly  distended.  The 
most  proximal  nodes  are  apt  to  be  overdistcnded,  but  for  this  very  reason  are  often 
excellent  for  the  study  of  the  reticular  tissue  from  which  most  of  the  cells  have 
been  washed  out,  especially  in  the  medulla. 

(3)  Human  lymph  nodes  maybe  treated  by  cither  of  the  above  mcthofls.  Ow- 
ing to  the  coalescence  of  their  cortical  nodules  their  structure  is  not  so  easily 
demonstrated  as  that  of  the  lymph  nodes  of  lower  animals. 


LYMPHATIC  ORGANS. 


151 


Haemolymph  Nodes. 

These  are  lymphoid  structures  which  closely  resemble  ordinary 
Ivmph  nodes,  but  with  the  essential  difference  that  their  sinuses  are 
blood  sinuses  instead  of  lymph  sinuses. 

Each  node  is  surrounded  by  a  capsule  of  varying  thickness,  com- 
posed of  fibro-elastic  tissue  and  smooth  muscle  cells.  From  the  cap- 
sule trabecula  of  the  same  structure  pass  down  into  the  node,  forming 
its  framework  (Fig.  88).  Beneath  the  capsule  is  a  blood  sinus,  which 
may  be  broad  or  narrow,  and  usually  completely  surrounds  the  node. 
Less  commonly  the  sinus  is  interrupted  by  lymphoid  tissue  extending 


Fig.  88. — Section  through  Human  H;emolymph  Node,  including  Hikim,  showing  capsule, 
trabeculse,  sinuses  filled  with  blood,  and  lymph  nodules.     (\\'arthin.) 

out  to  the  capsule.  From  the  peripheral  sinus  branches  extend  into  the 
interior  of  the  node,  separating  the  lymphoid  tissue  into  cords  or  islands. 
The  relative  proportion  of  sinuses  and  lymphoid  tissue  varies  greatly, 
some  nodes  being  composed  almost  wholly  of  sinuses,  while  in  others 
the  lymphoid  tissue  predominates.  There  is  usually  a  fairly  distinct 
hihim.  In  many  glands  no  differentiation  into  cortex  and  medulla  can 
be  made.  Where  there  are  a  distinct  medulla  and  cortex  the  peripheral 
lymphoid  tissue  is  arranged  in  nodules  as  in  the  ordinary  lym])h  node. 
Reticular  connective  tissue  crosses  the  sinuses  and  supports  the  cells  of 
the  lymph  nodules  and  cords  (Fig.  89). 


152 


THE  ORGANS. 


The  cellular  character  of  the  lymphoid  tissue  has  led  to  the  sub- 
division of  hasmolymph  nodes  into  splenolymph  nodes  and  marrow- 
lymph  nodes.  In  the  splenolymph  node  the  lymphoid  tissue  resembles 
that  of  the  ordinary  lymph  node  of  the  spleen.  In  the  marrow- 
lymph  node,  which  is  the  much  less  common  form,  the  lymphoid 
tissue  resembles  red  marrow.  There  are  no  distinct  nodules,  and 
there  is  a  quite  characteristic  distribution  of  small  groups  of  fat  cells. 
The  most  numerous  cells  are  eosinophiles  and  mast  cells  (see  page 
98).     Polynuclear    leucocytes    and    large    leucocytes    with    a    single 


Fig.  89. — Section  through  Superficial  Portion  of  Human  Hffimolymph  Node  (Marrow- 
lymph  Node).  (Warthin.)  Capsule,  trabecuiae,  and  parts  of  two  adjacent  nodules;  sinuses 
filled  with  blood;  among  the  lymph  cells  are  large  multinuclear  cells  resembling  those  of 
marrow,  nucleated  red  blood  cells,  etc. 


lobulated  nucleus  are  less  numerous.  The  very  large  multinuclear 
cells  of  red  marrow  are  also  found,  but  usually  in  small  numbers. 

Large  phagocytes  containing  blood  pigment  and  disintegrating  red 
blood  cells  are  found  in  both  forms  of  haemolymph  nodes,  but  are 
most  numerous  in  the  splenolymph  type.  In  nodes  which  have  a 
brownish  color  when  fresh,  these  phagocytes  frequently  almost  com- 
pletely fill  the  sinuses. 

Further  classification  of  haemolymph  nodes  has  been  attempted, 
but  is  unsatisfactory,  owing  to  the  large  number  of  transitional  forms. 
Thus  many  nodes  are  transitional  in  structure  between  the  haemo- 
lymph node  and  the  ordinary  lymph  node,  between  the  splenolymph 


LYIMPHATIC  ORGANS.  153 

node  and  the  marrowlymph  node,  and  between  the  splenolymph 
node  and  the  spleen. 

Under  normal  conditions  the  hsemolymph  nodes  appear  to  be 
concerned  mainly  in  the  destruction  of  red  blood  cells;  possibly  also 
in  the  formation  of  leucocytes.  Under  certain  pathological  con- 
ditions they  probably  become  centres  for  the  formation  of  red  blood 
cells. 

Blood-vessels. — An  artery  or  arteries  enter  the  node  at  the  hilum, 
and  break  up  within  the  node  into  small  branches,  which  communi- 
cate with  the  sinuses  where  the  blood  comes  into  intimate  association 
with  the  lymphoid  tissue.  From  the  sinuses  the  blood  passes  into 
veins,  which  leave  the  organ  either  at  the  hilum  or  at  some  other 
point  on  the  periphery.  The  course  which  the  blood  takes  in  pass- 
ing through  the  haemolymph  node  is  thus  apparently  similar  to  that 
taken  by  the  lymph  in  passing  through  the  ordinary  lymph  node. 

The  relation  of  the  haemolymph  node  to  the  lymphatic  system  is 
not  known,  and  like  ignorance  exists  as  to  its  innervation. 

TECHNIC. 

Same  as  for  lymph  nodes  (technic  i,  p.  150).  The  nodes  are  found  in  greatest 
numbers  in  the  prevertebral  tissue,  and  are  often  difficult  to  recognize.  Fixing  the 
tissues  in  5-per-cent.  formalin  aids  in  their  recognition  as  it  darkens  the  nodes  while 
bleaching  the  rest  of  the  tissues. 

The  Thymus. 

The  thymus  is  an  organ  of  fcetal  and  early  extra-uterine  life; 
reaching  in  man  its  greatest  development  at  the  end  of  the  second 
year.  After  this  age  it  undergoes  a  slow  retrograde  change  into  fat 
and  connective  tissue,  until  by  the  twentieth  year  scarcely  a  vestige 
of  glandular  tissue  remains. 

The  thymus  originates  in  the  entoderm  and  begins  its  foetal  exist- 
ence as  a  typical  epithelial  gland.  Into  this  epithelial  structure  meso- 
dermic  cells  grow  and  differentiate  into  lymphatic  tissue.  This  almost 
completely  replaces  the  epithelial  tissue,  only  rudiments  of  which 
remain. 

Morphologically  tlie  fully  developed  thymus  consists  of  lobes  and 
lobules  (Fig.  90).  The  whole  gland  is  surrounded  by  a  connective- 
tissue  capsule,  and  the  lobes  are  separated  from  one  another  by  strong 
extensions  of  capsular  tissue.     Smaller  connective-tissue  septa  extend 


154  THE  ORGANS. 

into  the  lobes,  subdividing  them  into  lobules.  From  the  perilobular 
connective  tissue,  septa  extend  into  the  lobule,  incompletely  sepa- 
rating it  into  a  number  of  chambers.  Each  lobule  consists  of  a  cor- 
tical portion  and  a  medullary  portion.  The  cortex  consists  of  nodules 
of  compact  lymphatic  tissue  similar  to  those  found  in  the  lymph 
node.  These  occupy  the  chambers  formed  by  the  connective-tissue 
septa.  The  medulla  consists  of  a  more  diffuse  lymphatic  tissue  with 
no  connective-tissue  septa.  It  is  common  for  the  medullary  tissue  to 
extend  to  the  surface  of  a  nodule  at  one  or  more  points  and  to  be  there 


FlG.   90. — From  Seclion  of  Human  Thymus,  showing  parts  of  five  lobules  and  interloljuiar 
septa.      X20.      (Technic,  page  155.)     a,  Corte.x;  b,  medulla;  c,  interlobular  septum. 

continuous  with  the  medullary  substance  of  an  adjacent  lobule.  In 
the  medulla  are  found  a  number  of  spherical  or  oval  bodies  composed 
of  concentrically  arranged  epithelial  cells.  These  are  known  as 
HassaWs  corpuscles  (Fig.  91),  and  represent  the  only  remains  of  the 
original  glandular  epithelium.  They  are  characteristic  of  the  thymus. 
The  central  cells  of  the  corpuscles  are  usually  spherical  and  contain 
nuclei,  while  the  peripheral  cells  are  flat  and  non-nucleated.  As  the 
entire  corpuscle  takes  a  bright  red  stain  with  eosin-hiemat(;xylin,  the 
corpuscles  stand  out  sharply  from  the  surrounding  bluish  lymphatic 
tissue.  With  low  magnifications  they  are  apt  to  be  mistaken  for  blood- 
vessels. 


LYMPHATIC  ORGANS.  1.55 

Unlike  the  other  lymphatic  organs,  the  lymph  nodules  of  the 
thymus  contain  no  germinal  centres.  Mitosis  can,  however,  usually 
be  seen  in  the  lymphoid  cells.  Nucleated  red  blood  cells  also  occur 
in  the  thymus.  The  thymus  must  therefore  be  considered  one  of  the 
sources  of  lymphoid  cells  and  of 
red  blood  cells.  ^-,:./ 

Blood-vessels. — The  larger 
arteries  run  in  the  connective- 
tissue  septa.  From  these,  smaller 
intralobular  branches  are  given 
off,  which  break  up  into  capillary 
netw^orks  in  the  cortex  and  me- 
dulla.    The  capillaries  pass  over  - 

into  veins.      These  converge  to  ''^*"^;  j-f^ 

form  larger  veins,  which  accom-  -- _^    ^j, 

pany  the  arteries.  ^^'^-    9^- — Hassall's    Corptiscle    and     Small 

„.       ,         ,  1       ,.  -      1  Portion    of    Surrounding    Tissue.       X6oo. 

Of     the     lymphatics     of    the  (See  Technic  below.) 

thymus   little   is   known.      They 

appear  to  originate  in  indefinite  sinuses  within  the  lymphoid  tissue, 
whence  they  pass  to  the  septa  where  they  accompany  the  blood-vessels. 
Nerves. — These  are  distributed  mainly  to  the  walls  of  the  blood- 
vessels. A  few  fine  fibres,  terminating  freely  in  the  lymphatic  tissue 
of  the  cortex  and  of  the  medulla,  have  been  described. 

TECHNIC. 

Fix  the  thymus  of  a  new-born  infant  in  formalin-Miiller's  fluid  (technic  5,  p. 
7),  and  harden  in  alcohol.  Stain  sections  with  htematoxylin-eosin  (technic  i, 
p.  i8),  or  with  haimatoxylin-picro-acid-fuchsin  (technic  3,  p.  19),  and  mount  in 
balsam. 

The  Tonsils. 

The  Palatine  Tonsils  or  True  Tonsils. — These  are  compound 
lyDipJiatic  organs,  essentially  similar  in  structure  to  tlic  Ivmphatic 
organs  already  described.  The  usual  fibrous  capsule  is  present  only 
over  the  attached  surface,  where  it  separates  the  tonsil  from  surround- 
ing structures.  From  the  capsule,  connective-tissue  trabeculcc  extend 
into  the  substance  of  the  organ  and  branch  to  form  its  framework. 
The  free  surface  of  the  tonsil  is  covered  by  a  reflection  of  the  stratified 
squamous  epithelium  of  the  pharynx  (Fig.  92).     The  epithelium  is  sepa- 


156  THE  ORGANS. 

rated  from  the  underlying  lymphatic  tissue  of  the  tonsil  by  a  more  or 
less  distinct  basement  membrane.  At  several  places  on  the  surface  of  the 
tonsil  deep  indentations  or  pockets  occur.  These  are  known  as  the 
crypts  of  the  tonsil  (Fig.  92),  and  are  lined  throughout  by  a  continuation 
of  the  surface  epithelium  which  becomes  thinner  as  the  deeper  part  of 
the  crypt  is  reached.  Passing  off  from  the  bottoms  and  sides  of  the 
main  or  primary  crypts  are  frequently  several  secondary  crypts,  also 
lined  with  the  same  type  of  epithelium. 


/  -":^' 


M. 


■im 


V 


Fig.  92. — ^Vertical  Section  of  Dog's  Tonsil  through  Crypt.  X15.  (Szymonowicz.) 
a,  Lymph  nodule;  b,  epitheh'um  of  crypt;  c,  blood-vessel;  d,  crypt;  e,  connective-tissue  cap- 
sule;/, mucous  glands;  g,  epithelium  of  pharynx. 

Beneath  the  basement  membrane  is  the  lymphoid  tissue  of  the 
tonsil.  This  consists  of  diffuse  lymphatic  tissue  in  which  are  found 
nodules  of  compact  lymphatic  tissue  similar  to  those  in  the  lymph  node. 
Each  nodule  has  a  ^erm  centre,  where  active  mitosis  is  going  on,  and  a 
surrounding  zone  of  more  densely  packed  cells.  The  nodules  have  a 
fairly  definite  arrangement,  usually  forming  a  single  layer  beneath 
the  epithelium  of  the  crypts.     At  various  points  on  the  surface  of  the 


LYMPHATIC  ORGANS. 


157 


tonsil,  and  especially  in  the  crypts,  occurs  what  is  known  as  lymphoid 
infiltration  of  the  epithelium  (Fig.  93).  This  consists  in  an  invasion  of 
the  epithelium  by  the  underlying  lymphoid  cells.  It  varies  from  the 
presence  of  only  a  few  lymphoid  cells  scattered  among  the  epithehal,  to 
an  almost  complete  replacement  of  epithelial  by  lymphoid  tissue.  In 
this  way  the  latter  reaches  the  surface  and  lymphoid  cells  are  dis- 
charged upon  the  surface  of  the  tonsil  and  into  the  crypts.  These  cells 
probably  form  the  bulk  of  the  so-called  salivary  corpuscles.  In  the 
connective  tissue  adjacent  to  the  tonsil  are  numerous  mucous  glands, 
the  ducts  of  which  empty  into  the  tonsillar  crypts. 

The  Lingual  Tonsils — Folliculi  Linguales. — These  are  small 
lymphatic  organs  situated  on  the  dorsum  and  sides  of  the  back  part 
of  the  tongue  between  the  circumvallate  papillae  and  the  epiglottis. 


Fig.  93. — Vertical  Section  through  \\"all  of  Crypt  in  Dog's  Tonsil,  showing  lymphoid 
infiltration  of  epithelium.  X150.  (Bohm  and  von  Davidoff.)  a,  Leucocytes  in  epithe- 
lium; b,  space  in  epithelium  filled  with  leucocytes  and  changed  epithelial  cells;  c,  blood-ves- 
sel; d,  epithelium  beyond  area  of  infiltration;  e,  basal  layer  of  cells. 

They  are  similar  in  structure  to  the  true  tonsils.  Each  lingual  tonsil 
has  usually  one  rather  wide-mouthed  deep  crypt  (the  foramen  cceciim 
lingui)  which  may  be  branched  and  which  is  lined  with  a  continuation 
of  the  surface  stratified  squamous  epithelium.  Into  these  crypts  fre- 
quently open  the  ducts  of  some  of  the  mucous  glands  of  the  tongue. 

The  Pharyngeal  Tonsils. — These  are  lymphatic  structures  which 
lie  in  the  naso-pharynx.  They  resemble  the  lingual  tonsils,  except 
that  they  are,  as  a  rule,  not  so  sharply  circumscribed.  Hypertrophy 
of  the  pharyngeal  tonsils  is  common  especially  in  children,  gi\"ing  rise 
to  what  are  known  as  adenoids. 

The  tonsils  make  their  first  appearance  toward  tlic  end  of  the 
fourth  month  of  intra-utcrinc  life.  The  earliest  of  the  tonsillar  lymph- 
oid cells  are  white  blood  cells  which   have  migrated  from   the  ves- 


158  THE  ORGANS. 

sels  of  the  stroma  of  the  mucosa  and  have  infiltrated  the  surrounding 
connective  tissue.  Further  development  of  the  tonsil  is  by  prolif- 
eration of  these  cells.  The  crypts  are  at  first  solid  ingrowths  of  sur- 
face epithelium.     These  later  become  hollowed  out. 

The  blood-vessels  and  nerves  have  a  distribution  similar  to  those 
of  the  lymph  nodes,  but  enter  the  organ  along  its  entire  attached  side 
and  not  at  a  definite  hilum. 

Of  the  lymphatics  of  the  tonsil  little  is  known. 

TECHNIC. 

Normal  human  tonsils  are  so  rare,  owing  to  the  frequency  of  inflammation  of 
the  organ,  that  it  is  best  to  make  use  of  tonsils  from  one  of  the  lower  animals  (dog, 
cat,  or  rabbit).  Treat  as  in  technic  i,  p.  150,  care  being  taken  that  sections  pass 
longitudinally  through  one  of  the  crypts. 

The  Spleen. 

The  spleen  is  a  lymphatic  organ,  the  peculiar  structure  of  which 
appears  to  depend  largely  upon  the  arrangement  of  its  blood-vessels. 
The  surface,  except  where  the  organ  is  attached,  is  covered  by  a 


/^' 


e 

Fig.  94. — Section  through  Porti(jn  of  Cat's  Spleen,  to  sliow  general  tojaography.  X  15. 
(Technic  i,  p.  163.)  a,  Capsule;  /;,  .sei)ta  containing  blood-vessels;  c,  germinal  centres; 
d,  septa;  e,  lymph  nodules. 

serous  membrane,  the  periloneum  (page  235).  Beneath  this  is  a  cap- 
sule of  fibrous  tissue  containing  numerous  elastic  fibres  and  smooth 
muscle  cells.  From  the  capsule  strong  connective-tissue  septa,  simi- 
lar to  the  capsule  in  structure,  extend  into  the  interior  of  the  organ. 
These  branch  and  unite  with  one  another  to  form  very  incomplete 


LY.MPHATIC  ORC.AXS.  159 

anastomosing  chambers.     The  capsule  and  septa  form,  as  in  the  lymph 
node,  the  connective-tissue  frameu^ork  of  the  organ  (Fig.  94). 

The  chambers  incompletely  bounded  by  the  connective-tissue 
septa  are  filled  in  with  tissue  resembling  lymphatic  tissue,  composed 
of  reticular  connective  tissue,  lymphoid  cells,  and  other  varieties  of 
cells  described  on  p.  161.  This  tissue  constitutes  the  substantia 
propria  of  the  organ  and  is  everywhere  traversed  by  thin-walled  vas- 
cular channels,  the  tissue  and  vascular  channels  together  constituting 
the  splenic  pulp  (Fig.  95).  Compact  lymphatic  tissue  occurs  in  the 
spleen  as  spherical,  oval,  or  cyHndrical  aggregations  of  closely  packed 


Fig.  95. — Section  of  Human  Spleen,  including  portion  of  Malpighian  body  with  its 
artery  and  adjacent  splenic  pulp.  X300.  (Technic  2,  p.  163.)  a,  Malpighian  body; 
b,  pulp  cords,  c,  cavernous  veins;  h  and  c  together  constituting  the  splenic  pulp. 

lymphoid  cells.  These  are  known  as  Malpighian  bodies  or  splenic 
corpuscles  (Figs.  94  and  95)  and  are  distributed  throughout  the  splenic 
pulp.  Each  splenic  corpuscle  contains  one  or  more  small  arteries. 
These  usually  run  near  the  periphery  of  the  corpuscle;  more  rarely 
they  lie  at  the  centre.  Except  for  its  relation  to  the  blood-vessels, 
the  splenic  corpuscle  is  quite  similar  in  structure  to  a  lymph  nodule. 
It  consists  of  lymphoid  cells  so  closely  packed  as  completely  to  obscure 
the  underlying  reticulum.  In  a  child's  spleen  the  centre  of  each 
corpuscle  shows  a  distinct  germinal  centre  (see  page  148).  In  the  adult 
luiman  spleen  germ  centers  are  rarely  seen.  The  blood-\"essels  of 
the  spleen  have  a  very  characteristic  arrangement,  wliicli  must  l)e 
described  Ijefore  considerinsji;  further  the  minute  structure  of  ihe  organ. 


160 


THE  ORGANS. 


The  arteries  enter  the  spleen  at  the  hihim  and  divide,  the  branches 
following  the  connective-tissue  septa.  The  arteries  are  at  first  ac- 
companied by  branches  of  the  splenic  veins.  Soon,  however,  the 
arteries  leave  the  veins  and  the  septa,  and  pursue  an  entirely  separate 
course  through  the  splenic  pulp.  Here  the  adventitia  of  the  smaller 
arteries  assumes  the  character  of  reticular  tissue  and  becomes  infil- 
trated with  lymphoid  cells.     In  certain  animals,  as,  e.g.,  the  guinea- 


Spleen  sinus 


XX         Sheathed  artery 


Pulp  artery 


Pulp  vein 


Beginningof  in- 
terlobular vein 


Capillary  net- 
work of  nodule 


TrabeculcB 


Penicillus 


Central  artery 


\Lobul 


Hilus 


Reticulum 


Spleen  nodule 


Capsule 


Fig.  g6. — Scheme  of  Human  Spleen,  x,  Oijening  of  arterial  capillaries  into  spleen 
sinus;  xx, interruption  of  closed  blood  course  at  ends  of  arterial  capillaries,  at  margin  of 
nodule,  xxx.  For  sake  of  clearness,  sinus  is  placed  Um  far  from  margin  of  nodule. 
(Stohr). 


pig,  this  infiltration  is  continuous,  forming  long  cord-like  masses  of 
compact  lymphoid  tissue.  In  man,  the  adventitia  is  infiltrated  only 
at  points  along  the  course  of  an  artery.  This  may  take  the  form 
of  elongated  collections  of  lymphoid  cells — the  so-called  spindles — 
or  of  distinct  lymph  nodules,  the  already  mentioned  splenic  corpuscles. 
Although  usually  eccentrically  situated  with  reference  to  the  nodules, 
these  arteries  are  known  as  central  arteries.  They  give  rise  to  a  few 
capillaries  in  the  spindles,  to  a  larger  number  in  the  nodules.  Beyond 
the  latter  the  arteries  divide  into  thick  sheathed  terminal  arteries— 


LYMPHATIC  ORGANS. 


161 


1^/ 


If 


m 


J 


ellipsoids — which  do  not  anastomose,  but  He  close  together  Hke  the 
bristles  of  a  brush  or  penicillus.  The  terminal  arteries  break  up  into 
arterial  capillaries  which  still  retain  an  adventitia,  and  which  empty 
into  broader  spaces — sinuses  or  ampullcE — which  in  turn  empty  into 
the  cavernous  veins  of  the  splenic  pulp  (Fig.  95 ). 

The  Splenic  Pulp. — The  anastomosing  cavernous  veins  break 
up  the  diffuse  lymphatic  tissue  of  the  spleen  into  a  series  of  anasto- 
mosing cords  similar  to  those 
found  in  the  medulla  of  the  lymph 
node.  These  are  known  as  pulp 
cords    (Fig.    95),    and    with    the 

cavernous    veins    constitute,    as  ■    "■:3>  ^ 

already  mentioned,  the  splenic 
pulp.     The  pulp  cords  consist  of  £'         /<^k 

a  delicate  framework  of  reticular 
connective  tissue,  in  the  meshes 
of  which  are  found,  in  addition 
to  lymphoid  cells,  the  following 

(Fig.  97) : 

(i)  Red  blood  cells. 

(2)  Nucleated  red  blood  cells. 

(3)  White  blood  cells. 

(4)  Mononuclear  cells,  the  so- 
called  spleen  cells.  These  are 
rather  large,  granular,  spherical,  or  irregular  cells.  From  the  fact  that 
blood  pigment  and  red  blood  cells  in  various  stages  of  disintegration 
are  found  in  their  cytoplasm,  these  cells  are  believed  to  be  concerned 
in  the  destruction  of  red  blood  cells. 

(5)  Multinuclear  cells.  These  are  most  common  in  young  ani- 
mals. Each  cell  contains  a  single  large  lobulated  nucleus,  or  more 
frequently  several  nuclei.  These  cells  resemble  the  osteoclasts  of 
developing  bone  and  the  multinuclear  cells  of  bone-marrow. 

In  macerated  splenic  tissue  or  in  smears  from  the  spleen,  there 
are  found,  in  addition  to  the  above  varieties  of  cells,  long  spindle- 
shaped  cells  with  bulging  nuclei.  These  come  from  the  walls  of  the 
cavernous  veins. 


F 


Fig.  97. — Isolated  Spleen  Cells.  X700. 
(Kolliker.)  A,  Cell  containing  red  blood 
cells;  b,  blood  cell;  k,  nucleus;  B,  leucocyte 
with  polymorphous  nucleus;  C,  "spleen"' 
cell  with  pigment  granules;  D,  lympho- 
cyte; E,  large  cell  with  lobulated  nucleus 
(megalocyte) ;  F,  nucleated  red  blood  cells; 
G,  red  blood  cell;  U,  multinuclear  leuco- 
cyte; J,  cell  containing  eosinophile granules. 


Two  views  are  held  regarding  the  vascular  channels  of  the  splenic  pulp.  Accord- 
ing to  one,  these  channels  have  complete  walls,  the  arterial  capillaries  passing  over 
into  venous  capillaries  in  the  usual  manner;  according  to  the  other,  the  arterial 
capillaries  open  into  spaces,  the  cavernous  veins  or  spleen  sinuses,  which  have 


162 


THE  ORGANS. 


fenestrated  walls,  thus  allowing  the  blood  to  come  into  direct  contact  with  the 
surrounding  tissues.  From  these  open-walled  sinuses,  the  veins  proper  take  origin. 
These  uniting  form  veins  which  enter  the  septa  and  ultimately  converge  to  form 
the  splenic  veins  which  leave  the  organ  at  the  hilum. 

According  to  Mall,  the  spleen,  like  the  liver,  is  composed  of  a  large  number  of 
lobules,  which  may  be  considered  its  anatomical  units  (Fig.  98).  Each  lobule  is 
separated  from  its  neighbors  by  several  (usually  three)  connective-tissue  septa 
(interlobular  septa).     Each  interlobular  septum  gives  off  about  three  secondary 

septa  (intralobular  septa)  which 
pass  into  the  lobule  and,  anasto- 
mosing, divide  it  into  about  ten 
chambers,  which  are  filled  with 
splenic  pulp.  As  the  splenic  pulp 
of  neighboring  chambers  anasto- 
moses, cord-like  structures  are 
formed  which  Mall  designates 
pulp  cords.  It  will  be  seen  that 
the  pulp  cords  of  Mall  are  alto- 
gether different  from  the  pulp 
cords  previously  mentioned.  An 
artery  passes  through  the  centre  of 
each  lobule,  giving  off  a  branch  to 
each  of  its  chambers.  These 
branch  repeatedly  in  the  pulp 
cords  of  Mall  and  end  in  small 
dilatations,  the  ampullae  of  Thoma. 
The  ampullae  pass  over  into  minute 
veins  which  converge  and  empty 
into  the  interlobular  veins.  Mall 
believes  the  walls  of  the  ampullae 
and  beginning  venous  plexuses  to  be  very  porous,  "allowing  fluids  to  pass  through 
with  great  ease,  and  granules  only  with  difficulty."  He  further  states  that  "in 
life  the  plasma  constantly  flows  through  the  intercellular  spaces  of  the  pulp  cords, 
while  the  blood  corpuscles  keep  within  fixed  channels." 


d 


-f 


Fig.  98. — Diagram  of  .bplenic  Lobule,  according  to 
Mall,  a,  Capsule;  b,  intralobular  venous  spaces; 
c,  intralobular  vein;  d,  ampulla  of  Thoma;  e, 
pulp  cord;  /,  interlobular  vein;  g,  intralobular 
vein;  h,  Malpighian  body;  f,  intralobular  tra- 
becula;  j,  interlobular  trabecula;  k,  intralobular 
artery;  /,  artery  to  one  of  the  ten  compartments; 
m,  intralobular  trabecula. 


Lymphatics  are  not  numerous.  In  certain  of  the  lower  animals 
large  lymph  vessels  occur  in  the  capsule  and  septa.  These  are  not 
well  developed  in  man.  Lymph  vessels  are  present  in  the  connective 
tissue  of  the  hilum.  They  probably  do  not  occur  in  the  splenic  pulp 
or  in  the  splenic  corpuscles. 

Nerves. — These  are  mainly  non-medullated,  although  a  few 
medullated  fibres  are  present.  Among  the  latter  are  dendrites  of 
sensory  neurones  whose  cell  bodies  are  situated  in  the  spinal  gan- 
glia. They  supply  the  connective  tissue  of  the  capsule,  septa,  and 
blood-vessels.     The    non-medullated    fibres — axones    of    sympathetic 


LYMPHATIC  ORGANS.  163 

neurones — accompany  the  arteries,  around  which  they  form  plexuses. 
From  these  plexuses  terminals  pass  to  the  muscle  cells  of  the  arteries, 
to  the  septa,  to  the  capsule,  and  possibly  also  to  the  splenic  pulp. 
The  exact  manner  in  which  both  medulla  ted  and  non-medullated 
fibres  terminate  is  as  yet  undetermined. 

TECHNIC. 

(i)  The  spleen  of  a  cat  is  more  satisfactory  for  topography  than  the  human 
spleen,  as  it  is  smaller,  contains  more  connective  tissue,  and  its  Malpighian  bodies 
are  more  evenly  distributed  and  more  circumscribed.  Fix  in  formalin-Miiller's 
fluid  (technic  5,  p.  7),  and  harden  in  alcohol.  Cut  sections  through  the  entire 
spleen.  Stain  with  hjematoxylin-eosin  (technic  i,  p.  18),  or  with  haematoxylin- 
picro-acid-fuchsin  (technic  3,  p.  19). 

(2)  Human  Spleen. — Small  pieces  are  treated  as  in  technic  (i). 

(3)  Human  Spleen  (Congested). — Congested  human  spleens  are  usually  easy 
to  obtain  from  autopsies.  Treat  as  in  technic  (i).  The  cavernous  veins  being  dis- 
tended with  blood,  the  relations  of  the  veins  to  the  pulp  cords  are  more  easily  seen 
than  in  the  uncongested  spleen.  The  contrasts  are  especially  sharp  in  sections 
stained  with  hasmatoxylin-picro-acid-fuchsin. 

(4)  The  cells  of  the  spleen  may  be  studied  along  the  torn  edges  or  in  the  thin- 
ner parts  of  any  of  the  spleen  sections.  Or  a  smear  may  be  made  in  a  manner 
similar  to  that  described  in  technic  (page  100),  by  drawing  the  end  of  a  slide  across 
a  freshly  cut  spleen  surface  and  then  smearing  the  tissue  thus  obtained  across  the 
surface  of  a  second  slide.  Dry,  fix  in  equal  parts  alcohol  and  ether  (one-half  hour), 
stain  with  haematoxylin-eosin  and  mount  in  balsam.  Or  the  cut  surface  of  the 
spleen  may  be  scraped  with  a  knife,  the  scrapings  transferred  to  Zenker's  fluid, 
hardened  in  alcohol,  stained  with  alum-carmine  (pages  17  and  57)  and  mounted  in 
eosin-glycerin. 

General  References  for  Further  Study. 

Kolliker:  Handbuch  der  Gewebelehre  des  [Menschen,  vol.  iii. 

Szymonowicz  and  MacCallum:  Histology  and  ^Microscopic  Anatomy. 

Warthin:  Haemolymph  Glands  (with  bibliography).  Reference  Handbook  of 
the  Medical  Sciences,  vol.  iv. 

Mall:  Lobule  of  the  Spleen.  Bui.  Johns  Hopkins  Hospital,  vol.  ix. — Archi- 
tecture and  Blood-vessels  of  the  Dog's  Spleen.     Zeit.  f.  Morph.  u.  Anth.,  Bd.  ii. 

Oppel:  Ueber  Gitterfasern  der  menschlichcn  Leber  und  ^Slilz.  Anat.  Anz.,  6 
Jahrg.,  S.  165. 


CHAPTER  III. 

THE  SKELETAL  SYSTEM. 

The  skeletal  system  consists  of  a  series  of  bones  and  cartilages 
which  are  united  by  special  structures  to  form  the  supporting  frame- 
work of  the  body.  Under  this  head  are  considered:  (i)  bones,  (2) 
marrow,  (3)  cartilages,  (4)  articulations. 

The  Bones. 

A  bone  considered  as  an  organ  consists  of  bone  tissue  laid  down 
in  a  definite  and  regular  manner.  If  a  longitudinal  section  be  made 
through  the  head  and  shaft  of  a  long  bone,  the  head  of  the  bone  and 
also  part  of  the  shaft  are  seen  to  be  composed  of  anastomosing  bony 
trabeculae  enclosing  cavities.     This  is  known  as  cancellous  or  spongy 


V\c,.  99. — Section  of  Spongy  Bone.     X75.    (Technic    3,  p.   172.)     a,  Marrow  space;  /), 
group  of  fat  cells;  c,  blood-vessel;  d,  trabeculse  of  bone. 

bone.  The  shaft  of  the  bone  consists  of  a  large  central  cavity  sur- 
rounded by  spongy  bone,  which,  however,  passes  over  on  its  outer 
side  into  a  layer  of  bone  of  great  density  and  known  as  hard  or  compact 
hone.  Spongy  bone  forms  the  ends  and  lines  the  marrow  cavities  of 
the  long  bones,  and  occurs  also  in  the  interior  of  short  bones  and  fiat 

1()4 


THE  SKELETAL  SYSTEM. 


165 


bones.  Compact  bone  forms  the  bulk  of  the  shafts  of  the  long  bones 
and  the  outer  layers  of  the  fiat  and  short  bones. 

In  compact  hone  the  layers  or  lamellae  of  bone  tissue  have  a  defi- 
nite arrangement  into  systems,  the  disposition  of  which  is  largely  de- 
pendent upon  the  shape  of  the  bone  and  upon  the  distribution  of  its 
blood-vessels. 

In  spongy  hone  (Fig.  99)  there  is  no  arrangement  of  the  bone  tissue 
into  systems.     The  trabeculae  consist  wholly  of  bony  tissue  laid  down 


Fig.   100. — Longitudinal  Section  of  Hard   (Undecalcified)  Bone:    Shaft  of  Human  Ulna. 
X  90.     (Szymonowicz.)     Haversian  canals,  lacuna;,  and  canaliculi  in  black. 

in  lamellae.  These  trabecules  anastomose  and  enclose  spaces  which 
contain  marrow  and  which  serve  for  the  passage  of  blood-vessels, 
lymphatics,  and  nerves. 

On  examining  a  longitudinal  section  of  compact  bone  (Fig.  100) 
there  are  seen  running  through  it  irregular  channels,  the  general 
direction  of  which  is  parallel  to  the  long  axis  of  the  bone.  These 
channels  anastomose  by  means  of  lateral  branches,  and  form  a  com- 
plete system  of  intercommunicating  tubes.  They  are  known  as  Haver- 
sian canals,  contain  marrow  elements,  and  serve  for  the  transmission 
of  blood-vessels,  Ivmplialics,  and  nerves.  They  anastomose  not  only 
with  one  another,  but  arc  in  communication  willi  the  surface  of  the 


166  THE  ORGANS. 

bone  and  with  the  central  marrow  cavity.     Between  the  Haversian 
canals  most  of  the  lamellae  run  parallel  to  the  canals. 

In  a  cross  section  through  the  shaft  of  a  long  bone  (Fig.  loi),  three 
distinct  systems  of  lamellae  are  seen.  These  are  known  as  Haversian 
lamellcB,  interstitial  lamellce,  and  circumferential  lamellce. 


. .  ~  ^   -  '^ 


Fig.  ioi. — Cross-section  of  Hard  (Undecalcified)  Bone  from  Human  Metatarsus. 
X  90.  (Szymonowicz.)  Haversian  canals,  lacuna;,  and  canaliculi  in  black,  a,  Outer 
circumferential  lamellae;  b,  inner  circumferential  lamella.-;  c,  Haversian  lamellae;  d,  in- 
terstitial lamellae. 

(i)  Haversian  Lamella  (Fig.  102). — These  are  arranged  in  a 
concentric  manner  around  the  Haversian  canals.  Between  the  lamellae, 
their  long  axes  corresponding  to  the  long  axes  of  the  Haversian  canals, 
are  the  lacunae  with  their  inclosed  hone  cells  (page  93).  The  lacunae  of 
adjacent  lamellae  are  usually  arranged  alternately.  In  a  section  of  or- 
dinary thickness  the  lacunae  arc  not  nearly  so  numerous  as  the  lamellae, 
and  are  seen  onlv  between  some  of  the  lamellae.     The  lacunas  of  a 


THE  SKELETAL  SYSTEM. 


IG- 


Haversian  system  communicate  with  one  another  and  with  their 
Haversian  canal  by  means  of  the  canalicidi.  In  Haversian  systems 
the  fibres  of  the  matrix  (see  page  93)  run  in  some  lamellae  parallel  to  the 
canal,  in  others  concentrically.  Adjacent  fibres  thus  frequently  cross 
at  right  angles. 

(2)  INTERSTITLA.L  (Intermediate  or  Ground)  Lamella.  (Figs, 
loi  and  102).— These  are  irregular  short  lamellse,  which  occupy  the 
spaces  left  between  adjacent 
Haversian  systems. 

(3)  Circumferential 
Lamella  (Fig.  loi). — These 
are  parallel  lamellae  which  run 
in  the  long  axis  of  the  bone, 
just  beneath  the  periosteum 
and  at  the  outer  edge  of  the 
central  marrow  ca\dty.  Oc- 
casionally circumferential 
lamellae  are  absent,  the 
Haversian  systems  abutting 
directly  upon  periosteum. 

Channels  for  the  passage 
of  blood-vessels  from  the  peri- 
osteum to  the  Haversian 
canals  pierce  the  circumferen- 
tial lamellae.  They  are  known 
as  V olkmann^ s  canals,  and  are 
not  surrounded  by  concentric 
lamellae  as  are  the  Haversian 
lamellae,  but  are  mere  chan- 
nels through  the  bone.  Similar 
canals  pass  from  the  inner  Haversian  canals  into  the  marrow  cavity. 

The  Periosteum. — This  is  a  fibrous  connective-tissue  membrane 
which  covers  the  surfaces  of  bones  except  where  they  articulate.  It 
is  firmly  adherent  to  the  superficial  layers  of  the  bone  and  consists 
of  two  layers.  The  outer  layer  is  composed  of  coarse  fibrillated  fibres 
and  contains  the  larger  blood-vessels.  The  inner  layer  consists  of 
fine  white  fibres  and  delicate  elastic  fibres  which  support  the  smaller 
blood-vessels. 

From  the  periosteum  distinct  bundles  of  white  fibres,  with  often 
some  elastic  fibres,  pierce  the  outer  layers  of  the  Ikjuc.     These  are 


Fig.  102. — Transverse  Section  of  Compact  Bone 
from  Shaft  of  Humerus.  X 1 50  and  slightly  re- 
duced. (Sharpey.)  (Technic  i,  p.  171.)  Three 
Haversian  canals  with  their  concentric  lamellse 
and  lacunas;  canaliculi  connecting  lacunsE  with 
each  other  and  with  Haversian  canal.  Between 
the  Haversian  systems  of  lamelke  are  seen  the 
interstitial  lamellfe. 


168  THE  ORGANS. 

known  as  the  perforating  fibres  of  Sharpey.  When  tendons  and  Kga- 
ments  are  attached  to  bone,  their  fibres  are  prolonged  through  the 
periosteum  into  the  bone  as  perforating  fibres. 

Bone  Marrow. 

Bone  marrow  is  a  soft  tissue  which  occupies  the  medullary  and 
Haversian  canals  of  the  long  bones  and  fills  the  space  between  the 
trabeculse  of  spongy  bone.  Marrow  occurs  in  two  forms — red  marrow 
and  yellow  marrow. 

Red  marrow  is  found  in  all  bones  of  embryos  and  of  young  ani- 
mals, also  in  the  vertebras,  sternum,  ribs,  cranial  bones,  and  epiphyses 
of  long  bones  in  the  adult.  In  the  diaphyses  of  adult  long  bones  the 
marrow  is  of  the  yellow  variety.  The  difference  in  color  between 
red  marrow  and  yellow  marrow  is  due  to  the  much  greater  proportion 
of  fat  in  the  latter,  yellow  marrow  being  developed  from  the  red  by 
an  almost  complete  replacement  of  its  other  elements  by  fat  cells. 

Red  marrow  is  of  especial  interest  as  a  blood-forming  tissue, 
being  in  the  healthy  adult  the  main  if  not  the  sole  source  of  red  blood 
cells,  and  one  of  the  sources  from  which  the  leucocytes  are  derived. 
The  blood-forming  function  of  marrow  must  be  borne  in  mind  in  study- 
ing the  various  forms  of  marrow  cells. 

Red  marrow  (Fig.  103)  consists  of  a  delicate  reticular  connective 
tissue  which  supports  the  following  varieties  of  cells: 

(i)  Marrow  Cells — Myelocytes. — These  resemble  the  mononu- 
clear and  some  of  the  transitional  forms  of  leucocytes.  The  nucleus 
is  large  and  may  be  lobulated.  It  contains  a  comparatively  small 
amount  of  chromatin  and  therefore  stains  faintly.  The  cytoplasm  is 
finely  granular  and  stains  with  neutrophile  dyes.  Myelocytes  are  not 
present  in  normal  blood,  but  occur  in  large  numbers  in  leukaemia. 
It  is  from  the  myelocytes  that  those  leucocytes,  which  are  of  bone- 
marrow  origin,  are  derived. 

{2)  Nucleated  Red  Blood  Cells. — These  are  divisible  into  erythro- 
blasts  and  normoblasts.  The  former  represents  an  earlier,  the  latter 
a  later  stage  in  the  evolution  of  the  non-nucleated  adult  red  blood 
cell. 

The  erythroblast,  the  younger  of  the  two,  has  a  well-formed  nu- 
cleus with  a  distinct  intranuclear  network.  The  protoplasm  contains 
Init  little  haemoglobin.  In  the  normoblast  the  intranuclear  network 
has    disappeared    and    the    protoplasm    has   become   much   richer  in 


THE  SKELETAL  SYSTEM. 


169 


hasmoglobin.  The  normoblast  is  converted  into  the  adult  red  blood 
cell  either  by  extrusion  of  its  nucleus  or  by  the  disintegration  of  the 
nucleus  within  the  cell  body. 

(3)  Non-nucleated  Red  Blood  Cells. — These  are  the  same  as  are 
found  in  the  blood  (page  95). 

(4)  Multimiclear  Cells — Myeloplaxes. — These  are  large  cells  with 
abundant  protoplasm.     Each  cell  may  contain  a  single  large  spheri- 


t    ... 

# 


M 


t*# 


f* 


^^  m 


^m 


--:---.d 


*^ 


g  f 

Fig.  103. — Section  of  Red  Bone-marrow  from  Rabbit's  Femur.  X  700.  (Technic  4> 
p.  172.)  a,  Red  blood  cells;  b,  myeloplax;  c,  fat  space;  d,  nucleated  red  blood  cells;  e, 
myelocytes;  /,  reticular  connective  tissue;  g,  leucocytes. 

cal  nucleus  or  a  much  lobulated  nucleus  or  several  nuclei.  Myelo- 
plaxes are  probably  derived  from  leucocytes,  and  are  closely  related 
to,  if  not  identical  with,  the  osteoclasts  of  developing  bone. 

(5)  Leucocytes  of  all  kinds  are  found  in  marrow.  They  ha\"c  the 
same  structure  as  in  blood  (page  96). 

(6)  Mast  cells  may  be  present.  They  are  usually  not  numerous. 
(For  description  see  page  98.) 

(7)  Fat  Cells. — These  are  usually  round  and  rather  c\"cnly  distrib- 
uted throughout  the  marrow. 


170 


THE  ORGANS. 


Yellow  marrow  (Fig.  104)  consists  almost  wholly  of  fat  cells, 
which  have  gradually  replaced  the  other  marrow  elements.  Under 
certain  conditions  the  yellow  marrow  of  the  bones  of  the  old  or  greatly 
emaciated  undergoes  changes  due  for  the  most  part  to  the  absorp- 
tion of  its  fat.  Such  marrow  becomes  red-dish  and  assumes  a  some- 
what gelatinous  appearance.     It  is  known  as  ^^  gelatinous  marrow^ 


f 

Fig.  104. — Yellow  Marrow  from  Rabbit's  Femur.  X560.  (Technic  4,  p.  172.)  a, 
nucleated  red  blood  cells;  h,  myeloplax,  c,  fat  cells;  d  myelocytes;  e,  reticular  connective 
tissue;/,  leucocytes. 

The  large  marrow  cavities,  such  as  those  of  the  shafts  of  the  long 
bones,  are  lined  by  a  layer  of  fibrous  connective  tissue,  the  endosteum. 

Blood-vessels. — The  blood-vessels  of  bone  pass  into  it  from  the 
periosteum.  Near  the  centre  of  the  shaft  of  a  long  bone  a  canal 
passes  obliquely  through  the  compact  bone.  This  is  known  as  the 
nutrient  canal  and  its  external  opening  as  the  nutrient  foramen.  This 
canal  serves  for  the  passage  of  the  nutrient  vessels^ — usually  one  artery 
and  two  veins — to  and  from  the  medullary  cavity.  In  its  passage 
through  the  compact  bone  the  nutrient  artery  gives  off  branches  to. 


THE  SKELETAL  SYSTEM.  171 

and  the  veins  receive  branches  from,  the  vessels  of  the  Haversian 
canals. 

Each  of  the  flat  and  of  the  short  bones  has  one  or  more  nutrient 
canals  for  the  transmission  of  the  nutrient  vessels. 

In  addition  to  the  nutrient  canals  the  surface  of  the  bone  is  every- 
where pierced  by  the  already  mentioned  (page  167)  Volkmann's 
canals,  which  serve  for  the  transmission  of  the  smaller  vessels.  In 
compact  bone  these  vessels  give  rise  to  a  network  of  branches  which 
run  in  the  Haversian  canals.  In  spongy  bone  the  network  lies  in 
the  marrow  spaces.  Branches  from  these  vessels  pass  to  the  marrow 
cavity,  and  there  break  up  into  a  capillary  network,  which  anasto- 
moses freely  with  the  capillaries  of  the  branches  of  the  nutrient  artery. 

The  capillaries  of  marrow  empty  into  wide  veins  without  valves, 
the  walls  of  which  consist  of  a  single  layer  of  endothelium.  So  thin 
are  these  walls  that  the  veins  of  marrow  were  long  described  as  pass- 
ing over  into  open  or  incompletely  walled  spaces  in  which  the  blood 
came  into  direct  contact  with  the  marrow  elements.  These  veins 
empty  into  larger  veins,  which  are  also  valveless.  Some  of  these  con- 
verge to  form  the  vein  or  veins  which  accompany  the  nutrient  artery; 
others  communicate  with  the  veins  of  the  Haversian  canals. 

Lymphatics  with  distinct  walls  are  present  in  the  outer  layer  of 
the  periosteum.  Cleft-like  lymph  capillaries  lined  with  endothelium 
accompany  the  blood-vessels  in  Volkmann's  and  in  the  Haversian 
canals.  The  lacunce  and  canalicuU  constitute  a  complete  system  of 
lymph  channels  which  communicate  with  the  lymphatics  of  the  perios- 
teum, of  Volkmann's  and  the  Haversian  canals,  and  of  the  bone- 
marrow. 

Nerves. — Both  medullated  and  non-medullated  nerves  accompany 
the  vessels  from  the  periosteum  through  Volkmann's  canals,  into  the 
Haversian  canals  and  marrow  cavities.  Pacinian  bodies  (page  388) 
occur  in  the  periosteum.  Of  nerve  endings  in  osseous  tissue  and  in 
marrow  little  definite  is  known. 

TECHNIC. 

(i)  Decalcified  Bone. — Fix  a  small  piece  of  the  shaft  of  one  of  the  long  bones 
— human  or  animal — in  formalin-^Iuller's  fluid  (technic  5,  p.  7),  and  decalcify  in 
hydrochloric  or  nitric  acid  solution  (page  10).  After  decalcifying,  wash  until  all 
traces  of  acid  are  removed,  in  normal  saline  solution  to  which  a  little  ammonia  has 
been  added.  Dehydrate,  and  embed  in  celloidin.  Transverse  and  longitudinal 
sections  are  made  through  the  shaft,  including  periosteum  and  edge  of  marrow 


172  THE  ORGANS. 

cavity.     Stain  with  hasmatoxylin-eosin   (technic   i,   p.    i8)   and  mount  in  eosin- 
glycerin. 

(2)  Hard  Bone. — Transverse  and  longitudinal  sections  of  undecalcified  bone 
may  be  prepared  as  in  technic  i,  p.  94. 

(3)  Spongy  Bone. — This  may  be  studied  in  the  sections  of  decalcified  bone, 
technic  (i),  where  it  is  found  near  the  marrow  cavity.  Or  spongy  bone  from  the 
head  of  one  of  the  long  bones  or  from  the  centre  of  a  short  bone  may  be  prepared 
as  in  technic  (2). 

(4)  Red  Marrow. — Split  longitudinally  the  femur  of  a  child  or  young  animal, 
and  carefully  remove  the  cylinder  of  marrow.  Fix  in  formalin-Muller's  fluid  and 
harden  in  graded  alcohols.  Cut  sections  as  thin  as  possible,  stain  with  haema- 
toxylin-eosin,  and  mount  in  balsam. 

(5)  Marrow:  fresh  specimen. — By  means  of  forceps  or  a  vice,  squeeze  out  a 
drop  of  marrow  from  a  young  bone,  place  on  the  centre  of  a  mounting  slide,  cover 
and  examine  it  immediately. 

(6)  Place  a  similar  drop  of  marrow  on  a  cover-glass  and  cover  with  a  second 
cover-glass.  Press  the  covers  gently  together,  slide  apart  and  fix  the  specimen  by 
immersion  for  five  minutes  in  saturated  aqueous  solution  of  mercuric  chlorid. 
Wash  thoroughly,  stain  with  hsematoxylin-eosin,  and  mount  in  balsam. 


Development  of  Bone. 

The  forms  of  bones  are  first  laid  down  either  in  cartilage  or  in 
embryonic  connective  tissue.  The  bones  of  the  trunk,  extremities, 
and  parts  of  the  bones  of  the  base  of  the  skull  develop  in  a  matrix 
of  cartilage.  This  is  known  as  intracartilaginous  or  endochondral 
ossification.  The  fiat  bones,  those  of  the  vault  of  the  cranium  and 
most  of  the  bones  of  the  face,  are  developed  in  a  matrix  of  fibrillar 
connective  tissue — intramembranous  ossification.  A  form  of  bone 
development,  similar  in  character  to  intramembranous,  occurs  in  con- 
nection with  both  intramembranous  ossification  and  intracartilaginous 
ossification.  This  consists  in  the  formation  of  bone  just  beneath  the 
perichondrium — subperichondrial  ossifiication — or,  as  with  the  de- 
velopment of  bone  perichondrium  l^ecomes  periosteum — subperiosteal 
ossifiication. 

There  are  thus  three  forms  of  bone  development  to  be  considered: 
(i)  Intramembranous,  (2)  intracartilaginous,  and  (3)  subperiosteal. 

I.  Intramembranous  Development  (Fig.  105). — In  intramem- 
branous ossification  the  matrix  in  which  the  bone  is  developed  is 
connective  tissue.  T'he  process  of  bone  formation  begins  at  one  or 
more  points  in  this  matrix.  These  are  known  as  ossification  centres. 
Here  some  of  the  bundles  of  white  fibres  become  calcifiied,  i.e.,  become 
impregnated  with  lime  salts.     There  is  thus  first  established  a  centre 


THE  SKELETAL  SYSTEM. 


173 


or  centres  of  calcification.  Between  the  bundles  of  calcified  fibres 
the  connective  tissue  is  rich  in  cells  and  vascular,  and  from  its  future 
role  in  bone  formation  is  known  as  osteogenetic  tissue  (Fig.  105).  Along 
the  surfaces  of  the  calcified  fibres  certain  of  the  osteogenetic  cells 
arrange  themselves  in  a  single  layer  (Figs.  105  and  106).  These  are 
now  known  as  osteoblasts  or  "bone  formers.'"  Under  the  influence 
of  these  osteoblasts  a  thin  plate  of  bone  is  formed  between  them- 


FiG.  105. — Intramembranous  Bone  Development.  Vertical  section  through  parietal 
bone  of  human  foetus.  Xi6o.  (Technic  i,  p.  179.)  a,  Osteoblasts;  b,  bone  trabecular; 
c,  osteoclasts  lying  in  Howship's  lacunae;  d,  internal  periosteum;  e,  bone  cells;/,  calcified 
fibres;  g,  osteogenetic  tissue;  h,  external  periosteum  (pericranium). 


selves  and  the  calcified  fibres.  This  plate  of  bone  at  first  contains  no 
cells,  but  as  the  lamella  of  bone  grows  in  thickness,  the  layer  of  osteo- 
blasts becomes  completely  enclosed  by  bone.  The  osteoblasts  are 
thus  transformed  into  bone  cells  (Fig.  106),  the  spaces  in  which  they 
lie  becoming  bone  lacimce.  The  bone  cell  is  thus  seen  to  be  derived 
from  the  embryonic  connective-tissue  cell,  the  osteoblast  being  an 
intermediate  stage  in  its  development.  In  this  way  irregular  anas- 
tomosing trabeculce  of  bone  are  formed  enclosing  spaces  (Fig.  105). 
The  bony  trabeculae  at  first  contain  remains  of  calcified  connective- 
tissue  fibres,  while  the  spaces,  which  are  known  as  primary  marrow 


174  THE  ORGANS. 

Spaces,  contain  blood-vessels,  osteogenetic  tissue,  and  developing 
marrow.  The  osteoblasts  ultimately  disappear  and  the  spaces  are 
then  occupied  by  blood-vessels  and  marrow.  The  connective-tissue 
membrane  has  now  been  transformed  into  cancellous  or  spongy  hone 

(Fig-  99)- 

The  bone  thus  formed  is  covered  on  its  outer  surface  by  a  layer 
of  connective  tissue,  a  part  of  tjbe  membrane  in  which  the  bone  was 
formed,  but  which  from  its  position  is  now  known  as  the  periosteum, 
or,  in  the  case  of  the  cranial  bones,  as  the  peri-  or  epicranium  (Fig.  105). 

In  this  form  of  bone  development,  occurring  as  it  does  in  the  bones 
of  the  skull,  provision  must  be  made  for  increase  in  the  size  of  the 

a  b 


Fig.  106. — Intramembranous  Bone  Development.  Vertical  section  through  parietal 
bone  of  human  foetus.  X  350.  (Technic  i,  p.  lyg.)  a,  Osteoblasts;  b,  calcified  fibres; 
c,  osteogenetic  tissue;  d,  osteoclast  lying  in  Howship's  lacuna;  e,  bone  lacunas;  /,  bone. 

cranial  ca\ity  to  accomodate  the  growing  brain.  This  is  accomplished 
in  the  following  manner:  Along  the  surface  of  the  bone,  directed 
toward  the  brain,  large  multinuclear  cells — osteoclasis  or  "  bone  breakers^' 
— make  their  appearance  (Fig.  106).  The  origin  of  these  cells  is  not 
clear.  Similar  cells  are  conspicuous  elements  of  adult  marrow.  They 
have  been  variously  described  as  derived  from  leucocytes,  from  osteo- 
blasts, or  directly  from  the  connective-tissue  cells.  A  recent  theory 
holds  that  they  are  derived  by  a  process  of  budding  from  the  endothelial 
cells,  which  form  the  walls  of  the  capillaries.  These  osteoclasts  appar- 
ently possess  the  power  of  breaking  down  bone.  They  are  found 
mainly  along  its  inner  surface,  and  can  be  seen  lying  in  little  depres- 
sions— Howship^s  lacuna  (Fig.  io6) — which  they  have  hollowed  out  in 
the  bone.  Between  the  outer  surface  of  the  bone  and  the  pericra- 
nium is  a  layer  of  osteogenetic  tissue,  the  innermost  cells  of  which  are 


THE  SKELETAL  SYSTEM. 


175 


arranged  as  osteoblasts  along  the  outermost  osseous  lamellae.  Here 
they  are  constantly  adding  new  bone  beneath  the  pericranium.  This 
new  bone  is  laid  down,  not  in  flat,  evenly  disposed  layers,  but  in  the  form 
of  anastomosing  trabeculas  enclosing  marrow  spaces. 

It  is  thus  seen  that  subperiosteal  bone, 
like  intramembranous,  is  at  first  of  the 
spongy  variety,  and  that  with  the  develop- 
ment of  the  cranium  the  original  intramem- 
branous bone  is  entirely  absorbed,  together 
with  much  of  the  subperiosteal. 

2.  Intracartilaginous  Development. — 
In  this  form  of  ossification  an  embryonal 
type  of  hyaline  cartilage  precedes  the  forma- 
tion of  bone,  the  cartilage  corresponding 
more  or  less  closely  in  shape  to  the  future 
bone  (Fig.  107).  Covering  the  surface  of  the 
cartilage  is  a  membrane  of  fibrillar  connec- 
tive tissue,  the  peridiondriiim  or  primary 
periosteum. 

In  most  of  the  long  bones  the  earliest 
changes  take  place  within  the  cartilage  at 
about  the  centre  of  the  shaft  (Fig.  107). 
Here  the  cartilage  cells  increase  in  size  and 
in  number  in  such  a  way  that  several  en- 
larged cartilage  cells  come  to  lie  in  a  single 
enlarged  cell  space,  and  the  cartilage  assumes 
the  character  of  hyaline  cartilage.  The  cell 
groups  next  arrange  themselves  in  rou's  or 
columns,  which  at  first  extend  outward  in  a 
radial  manner  from  a  common  centre,  but 
later  lie  in  the  long  axis  of  the  bone.  During 
these  changes  in  the  cells  there  is  an  increase 
in  the  intercellular  matrix  and  a  deposit  there 
of  calcium  salts.  In  this  way  the  cartilage 
becomes  calcified,   the  area  involved  being 

known  as  the  calcification  centre.  Further  growth  of  cartilage  at  the 
calcification  centre  now  ceases  and,  as  growth  of  cartilage  at  the  ends 
of  the  bone  continues,  the  central  portion  of  the  shaft  appears  con- 
stricted. The  changes  up  to  this  point  seem  to  be  preparatory  to 
actual  bone  formation. 


Fig 


7.  Inli'vK  a: ::..!.,;..'  'US 
Bone  iJevelopment.  Longi- 
tudinal section  of  one  of  the 
bones  of  embr\-o  sheep's  foot, 
showing  ossification  centre. 
X20.  (Technic  2,  p.  179.) 
a,  Periosteum;  b,  blood-ves- 
sels; c,  subperiosteal  bone; 
d,  intracartilaginous  bone;  e, 
osteogenetic  tissue:  /,  carti- 
lage; g,  ossification  centre:  h, 
calcification  zone. 


176 


THE  ORGANS. 


Ossification  proper  begins  by  blood-vessels  from  the  periosteum^ 
pushing  their  way  into  the  calcified  cartilage  at  the  calcification  centre, 
carrying  with  them  some  of  the  osteogenetic  tissue  from  beneath  the 
periosteum.  These  blood-vessels  with  their  accompanying  osteo- 
genetic tissue  are  known  as  periosteal  buds  (Fig.  io8).  Osteoblasts 
now  develop  from  the  osteogenetic  tissue  and  appear  to  dissolve  the 

calcified  cartilage  from  in  front 
of  the  advancing  vessels.  In  this 
way  the  septa  between  the  car- 
tilage cell  spaces  are  broken 
down,  the  cartilage  cells  disap- 
pear, and  a  central  cavity  is 
formed — the  primary  marrow 
cavity.  From  the  region  of  the 
primary  marrow  cavity  blood- 
vessels and  osteogenetic  tissue 
push  in  both  directions  toward 
the  ends  of  the  cartilage  which  is 
to  be  replaced  by  bone.  These 
break  down  the  transverse  septa 
between  the  cell  spaces,  while 
many  of  the  longitudinal  septa 
at  first  remain  to  form  the  walls 
of  long  anastomosing  channels, 
the  primary  marroiv  spaces  (Fig. 
109).  As  in  intramembranous 
bone,  these  contain  blood-vessels, 
embryonal  marrow,  and  osteo- 
blasts, all  of  which  are  derived 
from  the  osteogenetic  tissue 
brought  in  from  the  periosteum  by  the  periosteal  buds.  The  osteo- 
blasts next  arrange  themselves  in  a  single  layer  along  the  remains  of 
the  calcified  cartilage,  where  they  proceed  to  deposit  a  thin  layer  of 
bone  between  themselves  and  the  cartilage  (Fig.  no).  As  this 
increases  in  thickness  some  of  the  osteoblasts  are  enclosed  within  the 
newly  formed  bone  to  become  hone  cells,  while  the  remains  of  the 
cartilage  dimishes  in  amount  and  finally  disappears.  The  calcification 
centre  has  now  become  the  ossification  centre,  and  its  anastomosing 


b  ^       ■■'^' 

Fig.  108. — Intracartilaginous  Bone  Develop- 
ment. X350.  Showing  osteogenetic  tissue 
pushing  its  way  into  the  cartilage  (periosteal 
bud)  at  the  ossification  centre,  a,  Perios- 
teum; b,  cartilage  cell  spaces;  c,  periosteal 
bud;  d,  blood-vessel;  e,  cartilage  cells;  /,  car- 
tilage matrix. 


'The  term    "periosteum"  is  admissible  from  the  fact  that  the  first  bone  actually 
formed  is  beneath  the  perichondrium,  which  thus  becomes  converted  into  periosteum. 


THE  SKELETAL  SYSTEM. 


V 


osseous  trabecule,  with  their  enclosed  spaces  containing  osteogenetic 
tissue  and  marrow,  constitute  primary  ^p&ngy  bone. 

At  either  end  of  the  ossification  centre  the  cartilage  presents  a 
special  structure.  Nearest  the  centre  the  cell  spaces  are  enlarged, 
flattened,  arranged  in  rows  and  contain  shrunken  cells.  Some  of  the 
walls  break  down  and  irregular  spaces  are  formed.  The  ground 
substance  is  calcified.  Passing 
away  from  the  ossification  centre, 
the  cell  spaces  become  less  flat- 
tened, still  arranged  in  rows,  the 
contained  cells  larger,  and  there 
is  a  lesser  degree  of  calcification. 
This  area  passes  over  into  an  area 
of  hyaline  cartilage  which  blends 
without  distinct  demarcation  with 
the  ordinary  embryonal  cartilage 
of  the  rest  of  the  shaft.  The  area 
of  calcified  cartilage  at  either  end 
of  the  ossification  centre  is  known 
as  the  calcification  zone  and  every-  c 

where  precedes  the  formation  of  Fig.  109.— Intracartilaginous  Bone  Develop- 
ment. Same  specimen  as  Fig.  107  (  X350), 
showing  osteogenetic  tissue  pushing  its  way 
into  the  cartilage  and  breaking  it  up  into 
trabeculse;  also  formation  of  primary  mar- 
row spaces  and  disintegration  of  cartilage 
cells,  a.  Disintegrating  cartilage  cells;  b, 
cartilage  trabecula;  c,  osteogenetic  tissue  in 
primary  marrow  space;  d,  blood-vessels; 
e,  cell  spaces;  /,  cartilage  cells. 


true  bone  (Fig.  107). 

3.  Subperiosteal  or  subperi- 
chondrial  development  (Fig. 
107)  has  already  been  largely  de- 
scribed in  connection  with  intra- 
membranous  ossification,  and 
dift'ers  in  no  important  respect  from  the  latter.  It  always  accom- 
panies one  of  the  other  forms  of  ossification.  Bone  appears  beneath 
the  perichondrium  somewhat  earlier  than  within  the  underlying 
cartilage.  Beneath  the  perichondrium  is  a  layer  of  richly  cellular 
osteogenetic  tissue.  The  cells  of  this  tissue  nearest  the  cartilage 
become  osteoblasts  and  arrange  themselves  in  a  single  layer  along  its 
surface.  Under  their  influence  bone  is  laid  down  on  the  surface  of  the 
cartilage  in  the  same  manner  as  in  intramembranous  ossification. 

Intracartilaginous  and  subperiosteal  bone  can  be  easily  differen- 
tiated by  the  presence  of  cartilaginous  remains  in  the  former  and  their 
absence  in  the  latter. 

All  hone  is  at  first  of  the  spongy  variety.  When  this  is  to  be  converted 
into  compact  bone,  there  is  first  absorption  of  bone  by  osteoclasts, 


178 


THE  ORGANS. 


with  increase  in  size  of  the  marrow  spaces  and  reduction  of  their  walls 
to  thin  plates.     These  spaces  are  now  known  as  Haversian  spaces. 

Within  these  new  bone  is  deposited.  This  is  done  by  osteoblasts 
which  lay  down  layer  within  layer  of  bone  until  the  Haversian  space  is 
reduced  to  a  mere  channel,  the  Haversian  canal.  In  this  way  are  formed 
the  Haversian  canals  and  the  Haversian  systems  of  lamellce.  Some 
of  the  interstitial  lamellae  are  the  remains  of  the  spongy  bone  which 
was  not  quite  removed  in  the  enlargement  of  the  primary  marrow  spaces 
to  form  the  Haversian  spaces;  other  interstitial  lamellae  appear  to  be 
early  formed  Haversian  lamellae  which  have  been  more  or  less  replaced 
by  Haversian  lamellae  formed  later. 


Fig.  no. — Intracartilaginous  Bone  Development.  Same  specimen  as  Fig.  io7(X3So), 
showing  bone  being  deposited  around  one  of  the  trabeculse  of  cartilage,  a,  Blood-vessel;  b, 
bone;  c,  cartilage  remains;  d,  bone  cell;  e,  cartilage  cell  space;  /,  osteoblasts;  g,  osteogenetic 
tissue;  h,  lamella  of  bone;  i,  connective-tissue  cells;  j,  cartilage  cell. 


While  these  varieties  of  ossification  have  been  described,  we  would 
emphasize  the  essential  unity  of  the  process.  The  likeness  between 
intramembranous  and  subperiosteal  ossification  has  been  already 
noted.  The  differences  observed  in  intracartilaginous  ossification 
are  more  apparent  than  real.  In  intracartilaginous  ossification  the 
bone  is  developed  in  cartilage  but  not  from  cartilage.  As  in  intra- 
membranous and  in  subperiosteal  ossification,  intracartilaginous 
bone  is  developed  from  osteogenetic  tissue.  This  osteogenetic  tissue 
is  a  differentiation  of  embryonal  connective  tissue,  in  this  case  car- 
ried into  the  cartilage  from  the  periosteum  in  the  periosteal  buds.  In 
intramembranous  ossification  the  bone  is  developed  within  and  directly 


THE  SKELETAL  SYSTEM.  179 

from  the  embryonal  connective  tissue  of  which  the  membrane  is  com- 
posed. In  intracartilaginous  ossification  there  is  the  same  embryonal 
connective-tissue  membrane,  but  within  this  membrane  the  form 
of  the  bone  is  first  laid  down  in  embryonal  cartilage.  Surrounding  the 
cartilage  there  remains  the  embryonal  connective  tissue  of  the  mem- 
brane, now  perichondrium.  It  is  from  tissue  which  grows  into  the 
cartilage  from  this  membrane — embryonal  connective  tissue — that 
the  bone,  although  developed  in  cartilage,  is  formed. 

Growth  of  Bone. 

The  growth  of  intramembranous  bone  by  the  formation  of  suc- 
cessive layers  beneath  the  periosteum  has  been  already  described 
(page  174). 

Intracartilaginous  bones  grow  both  in  diameter  and  in  length. 

Growth  in  diameter  is  accomplished  by  the  constant  deposition 
of  new  layers  of  bone  beneath  the  periosteum.  During  this  process, 
absorption  of  bone  from  within  by  means  of  osteoclasts  leads  to  the 
formation  of  the  marrow  cavity.  The  hard  bone  of  the  shaft  of  a 
long  bone  is  entirely  of  subperiosteal  origin,  the  intracartilaginous 
bone  being  completely  absorbed. 

Growth  in  length  takes  place  in  the  following  manner:  Some  time 
after  the  beginning  of  ossification  in  the  shaft  or  diaphysis,  independent 
ossification  centres  appear  in  the  ends  of  the  bone  (epiphyses).  So 
long  as  bone  is  growing,  the  epiphyses  and  diaphysis  remain  distinct. 
Between  them  lies  a  zone  of  growing  cartilage,  the  epiphyseal  or  inter- 
mediate cartilage.  Increase  in  length  of  the  bone  takes  place  by  a 
constant  extension  of  ossification  into  this  cartilage  from  the  ossifi- 
cation centers  of  the  epiphyses  and  diaphysis.  After  the  bone  ceases  to 
grow  in  length,  the  epiphyses  and  diaphysis  become  firmly  united. 

TECHNIC. 

(i)  Developing  Bone — Intramembranous. — Small  pieces  are  removed  from 
near  the  edge  of  the  parietal  bone  of  a  new-born  child  or  animal.  These  pieces 
should  include  the  entire  thickness  of  bone  with  the  attached  scalp  and  dura  mater. 
Treat  as  in  technio  i,  p.  171,  except  that  the  sections  which  are  cut  perpendicular 
to  the  surface  of  the  bone  should  be  stained  with  ha?matoxylin-picro-acid-fuchsin 
(technic  3,  p.  19)  and  mounted  in  balsam. 

(2)  Developing  Bone — Intracartilaginous  and  Subperiosteal. — Remove  the 
forearms  and  legs  of  a  human  or  animal  embryo  by  cutting  through  the  elbow,  and 


ISO  THE  ORGANS. 

knee-joints.  (Fcetal  pigs  from  five  to  six  inches  long  are  very  satisfactory.)  Treat 
as  in  technic  (i).  Block  so  that  the  two  long  bones  will  lie  in  such  a  plane  that 
both  will  be  cut  at  the  same  time.  Cut  thin  longitudinal  sections  through  the  ossi- 
iication  centres,  stain  with  hasmatoxylin-picro-acid-fuchsin,  and  mount  in  balsam. 
Cut  away  the  ends  of  one  or  two  of  the  embedded  bones,  leaving  only  the  ossifica- 
tion centres.  Block  so  as  to  cut  transverse  sections  through  the  ossification  centre. 
Stain  and  mount  as  the  preceding. 

In  the  picro-acid-fuchsin  stained  sections  of  developing  bone  the  cartilage  is 
stained  blue;  cells,  including  red  blood  cells,  yellow;  connective  tissue  from  pale 
pink  to  red,  according  to  density;  bone  a  deep  red. 

The  Cartilages. 

The  costal  cartilages  are  hyaline.  They  are  covered  by  a  closely 
adherent  connective-tissue  membrane,  the  perichondrium.  Where 
cartilage  joins  bone  there  is  a  firm  union  between  the  two  tissues 
and  the  perichondrium  becomes  continuous  with  the  periosteum. 

The  articular  cartilages  are  described  below  under  articulations. 

The  other  skeletal  cartilages,  such  as  those  of  the  larynx,  trachea, 
bronchi,  and  of  the  organs  of  special  sense,  are  more  conveniently 
considered  with  the  organs  in  which  they  occur. 

Articulations. 

Joints  are  immovable  (synarthrosis)  or  movable  (diarthrosis).  In 
synarthrosis  union  may  be  cartilaginous  (synchondrosis),  or  by  means 
of  fibrous  connective  tissue  (syndesmosis). 

Synchondrosis. — The  cartilage  is  usually  of  the  fibrous  form 
except  near  the  edge  of  the  bone,  where  it  is  hyaline.  The  interver- 
tebral discs  consist  of  a  ring  of  fibro-cartilage  surrounding  a  central 
gelatinous  substance,  the  nucleus  pulposus,  the  latter  representing 
the  remains  of  the  notochord. 

Syndesmosis. — Union  is  by  means  of  ligaments.  These  may 
consist  wholly  of  fibrous  tissue,  the  fibres  and  cells  being  arranged 
much  as  in  tendon,  or  mainly  of  course  elastic  fibres  separated  by 
loose  fibrous  tissue.  In  such  syndesmoses  as  the  sutures  of  the  cranial 
bones,  the  union  is  by  means  of  short  fibrous  ligaments  between  the 
adjacent  serrated  edges. 

Diarthrosis. — In  diarthrosis  must  be  considered  '(a)  the  articular 
cartilages,  (b)  the  glenoid  ligaments  and  interarticular  cartilages,  (c) 
the  joint  capsule. 

(a)     Articular  cartilages  cover  the  ends  of  the  bones.     They  are 


THE  SKELETAL  SYSTE^L  l8l 

of  the  hyaline  variety/  being  the  remains  of  the  original  cartilaginous 
matrix  in  which  the  bones  are  formed.  Xext  to  the  bone  is  a  narrow 
strip  of  cartilage  in  which  the  matrix  is  calcified.  This  is  separated 
from  the  remaining  uncalcified  portion  of  the  cartilage  by  a  narrow 
so-called  "striated"  zone.  The  most  superficial  of  the  cartilage 
cells  are  arranged  in  rows  parallel  to  the  surface;  in  the  mid-region 
the  grouping  of  cells  is  largely  in  twos  and  fours  as  in  ordinary  hyaline 
cartilage  (page  90);  while  in  the  deepest  zone  of  the  uncalcified  carti- 
lage the  cells  are  arranged  in  rows  perpendicular  to  the  surface. 

(b)  The  glenoid  ligaments  and  interarticular  cartilages  conform 
more  to  the  structure  of  dense  fibrous  tissue  than  to  that  of  cartilage. 

(c)  The  joint  capsule  consists  of  two  layers,  an  outer  layer  of  dense 
fibrous  tissue  intimately  blended  with  the  ligamentous  structures 
of  the  joint  and  known  as  the  stratum  Jibrosum,  and  an  inner  layer, 
the  stratum  synoviale  or  synovial  membrane,  which  forms  the  lining 
of  the  joint  cavity.  The  outer  part  of  the  stratum  synoviale  consists 
of  areolar  tissue  with  its  loosely  arranged  white  and  elastic  fibres  inter- 
lacing in  all  directions  and  scattered  connective-tissue  cells  and  fat 
cells.  Nearer  the  free  surface  of  the  membrane  the  fibres  run  parallel 
to  the  surface  and  the  cellular  elements  are  more  abundant.  The 
cells  are  scattered  among  the  fibres  and  are  stellate  branching  cells 
like  those  usually  found  in  fibrous  connective  tissue.  On  the  free 
surface,  however,  the  cells  are  closely  packed  and  although  in  places 
often  several  layers  deep,  are  probably  of  the  nature  of  endothelium. 

From  the  free  surfaces  of  synovial  membranes,  processes  {synovial 
villi — Haversian  fringes)  project  into  the  joint  cavity.  Some  of 
these  are  non-vascular  and  consist  mainly  of  stellate  cells  similar  to 
those  of  the  synovial  membrane.  Others  have  a  distinct  core  of 
fibrous  tissue  containing  blood-vessels  and  covered  with  stellate  con- 
nective-tissue cells.  From  the  primary  villi  small  secondary  non- 
vascular villi  are  frec^uently  given  off. 

TECHNIC. 

(i)  Joint  Capsule  and  Articular  Cartilage. — Remove  one  of  the  small  joints — 
human  or  animal — cutting  the  bones  through  about  one-half  inch  back  from  the 
joint.  Treat  as  in  technic  i,  p.  171,  making  longitudinal  sections  through  the  en- 
tire joint. 

'  In  the  acromio-clavicular,  sterno-clavicular.  costo-vertebral,  and  maxillary  articula- 
tions the  cartilage  is  of  the  fibrous  form.  The  same  is  true  of  the  cartilage  covering  the 
head  of  the  ulna,  while  the  surface  of  the  radius,  which  enters  into  the  wrist-joint,  is 
covered  not  bv  cartilage,  but  bv  dense  fibrous  tissue. 


182  THE  ORGANS. 

(2)  Synovial  Villi. — Remove  a  piece  of  the  capsular  ligament  from  near  the 
border  of  the  patella  and  cut  out  a  bit  of  the  velvety  tissue  which  lines  its  inner 
surface.  Examine  fresh  in  a  drop  of  normal  salt  solution.  Fix  a  second  piece  of 
the  ligament  in  formahn-Muller's  fluid  (technic  5,  p.  7),  make  sections  perpendic- 
ular to  the  surface,  stain  with  haematoxylin-eosin  (technic  i,  p.  18),  and  mount 
in  balsam. 

General  References  for  Further  Study. 

KoUiker:  Handbuch  der  Gewebelehre,  vol.  i. 
Stohr:  Text-book  of  Histology. 

Schafer:  Histology  and  Microscopical  Anatomy,  in  Quain's  Elements  of 
Anatomy. 


CHAPTER  IV 
THE  MUSCULAR  SYSTEM/ 

The  voluntary  muscular  system  consists  of  a  number  of  organs — 
the  muscles — and  of  certain  accessory  structures — the  tendons,  tendcni 
sheaths,  and  hursa. 

A  VOLUNTARY  MUSCLE  coHsists  of  Striated  muscle  fibres  arranged 
in  bundles  or  fascicles  and  supported  by  connective  tissue. 

The  entire  muscle  is  enclosed  by  a  rather  firm  connective-tissue 
sheath  or  capsule — the  epimysium   (Fig.  in).     This  sends  trabeculae 


Fig.  I II. — From  a  Transverse  Section  of  a  Small  Human  Muscle,  showing  relations  of 
muscle  fibres  to  connective  tissue,  a,  Epimysium;  h,  perimysium;  c,  muscle  fibres;  d, 
arteries;  e,  endomysium. 

of  more  loosely  arranged  connective  tissue  into  the  substance  of  the 
muscle.  These  divide  the  muscle  fibres  into  bundles  or  fascicles. 
Around  each  fascicle  the  connective  tissue  forms  a  more  or  less  definite 

'  Definite  arrangements  of  smooth  muscle,  such  as  are  found  in  the  stomach  and  intes- 
tines, also  the  muscle  of  the  heart,  are  properly  a  part  of  the  muscular  system.  They  are, 
however,  best  considered  under  tissues  and  in  connection  with  the  organs  in  which  they 
occur. 

183 


184 


THE  ORGANS. 


I, 


v// 


/y  v/1 


.' ■•  (   I, 


,1  \l 


y^'>: 


'h    ''I  '      '^f  ft.  "■■'   'i' 


envelope,  the  perifasckidar  sheath  or  perimysium.  From  the  latter 
delicate  strands  of  connective  tissue  pass  into  the  fascicles  between 
the  individual  muscle  fibres.  This  constitutes  the  intrafascicular 
connective  tissue  or  endomysium,  which  everywhere  completely  separates 
the  fibres  from  one  another  so  that  the  sarcolemma  of  one  fibre  never 
comes  in  contact  with  the  sarcolemma  of  any  other  fibre.     It  should 

be  noted  that  these  terms  in- 
dicate merely  location;  epi-, 
peri-,  and  endo-mysium  all 
being  connective  tissue  grad- 
ing from  coarse  to  fine,  as 
it  passes  from  without  in- 
ward. The  structure  of  the 
muscle  as  an  organ  is  thus 
seen  to  conform  to  the  struc- 
ture of  other  organs,  in  that 
it  is  surrounded  by  a  con- 
nective-tissue capsule,  which 
sends  septa  into  the  organ, 
dividing  it  into  a  number  of 
compartments  and  serving 
for  the  support  of  the  essen- 
tial tissue  of  the  organ,  the 
Fig.   ii2.-From  a  longitudinal  Section  through  muscle  fibres  or  parenchvma. 

J  unction  of  Muscle  and  Tendon.     X  150.    (Bohm 

and  Davidoff.)     a,  Tendon;  h,  line  of  union  show-         The  Structure  of  tendon  has 

ing  increase  in  number  of  muscle  nuclei;  .,  muscle.    ^^^^  described  (see  page  78) . 

Tendon  sheaths  and  bursoe  are  similar  in  structure,  consisting  of 
mixed  white  and  elastic  fibres.  Their  free  surfaces  are  usually  lined 
by  fiat  cells,  which  are  described  by  some  as  connective-tissues  cells,  by 
others  as  endothelium. 

At  the  junction  of  muscle  and  tendon,  the  muscle  fibre  with  its 
sarcolemma  ends  in  a  rounded  or  blunt  extremity  (Fig.  58,  p.  106). 
Here  the  fibrils  of  the  tendon  fibres  are  in  part  cemented  to  the  sar- 
colemma, and  in  part  are  continuous  with  the  fibres  of  the  endo-  and 
peri-mysium.  Along  the  line  of  union  of  muscle  and  tendon  the  muscle 
nuclei  are  more  numerous  than  elsewhere  (Fig.  112,  h),  and  it  has  been 
suggested  that  there  is  here  a  zone  of  indiiTerent  or  formative  tissue 
which  is  capable  of  developing  on  the  one  hand  into  muscle,  on  the 
other  into  the  connective  tissue  of  tendon. 

Growth  of  muscle  takes  place  mainly  at  the  ends  of  the  fibres 


t0kif0mlM^M0^f'M 


THE  MUSCULAR  SYSTEM.  185 

where  the  nuclei  are  most  numerous.  In  addition  to  the  growth 
incident  to  increase  in  size  of  the  individual  or  of  the  particular  muscle, 
there  is  a  constant  wearing  out  of  muscle  fibres  and  their  replacement 
by  new  fibres.  This  is  accomplished  as  follows:  The  muscle  fibre 
first  breaks  up  into  a  number  of  segments  (sarcostyles),  some  of  which 
contain  nuclei  while  others  are  non-nucleated.  The  sarcostyles  next 
divide  into  smaller  fragments,  and  finally  completely  disintegrate. 
This  is  followed  by  a  process  of  absorption  and  complete  disappearance 
of  the  fibre.  From  the  free  sarcoplasm  new  muscle  fibres  are  formed. 
In  the  early  stages  of  their  development  these  are  known  as  myoblasts. 
The  latter  develop  into  muscle  fibres  in  the  same  manner  as  described 
under  the  histogenesis  of  muscle  (p.  loSj. 

Blood-vessels. — The  larger  arteries  of  muscle  run  in  the  perimy- 
sium, their  general  direction  being  parallel  to  the  muscle  bundles. 
From  these,  small  branches  are  given  ofl'  at  right  angles.  These  in 
turn  give  rise  to  an  anastomosing  capillary  network  with  elongated 
meshes,  which  surrounds  the  indi\"idual  muscle  fibres  on  all  sides. 
From  these  capillaries,  veins  arise  which  follow  the  arteries.  Even 
the  smallest  branches  of  these  veins  are  supplied  with  valves. 

In  tendons  blood-vessels  are  few.  They  run  mainly  in  the  connec- 
tive tissue  which  surrounds  the  fibre  bundles.  Tendon  sheaths  and 
bursae,  on  the  other  hand,  are  well  supplied  with  blood-vessels. 

The  lymphatics  of  muscle  are  not  numerous.  They  accompany 
the  blood-vessels.  In  tendon  definite  lymph  vessels  are  found  only  on 
the  surface. 

Nerves. — The  terminations  of  nerves  in  muscle  and  tendon  are 
described  under  nerve  endings  (page  388). 

TECHNIC. 

(i)  A  Muscle. — Select  a  small  muscle,  human  or  animal,  and,  attaching  a  weight 
to  the  lower  end  to  keep  it  stretched,  fix  in  formaHn-Miiller's  fluid  (technic  5,  p.  7), 
and  harden  in  alcohol.  Stain  transverse  sections  with  ha?mato.\ylin-])icro-acid- 
fuchsin  (technic  3,  p.  19)  and  mount  in  balsam. 

(2)  Junction  of  Muscle  and  Tendon. — Any  muscle-tendon  junction  may  be 
selected.  Fix  in  formalin-MuUer's  fluid,  keeping  stretched  by  means  of  a  weight 
attached  to  the  lower  end.  Cut  longitudinal  sections  through  the  muscle-tendon 
junction,  stain  with  hicmatoxylin-picro-acid-fuchsin,  and  mount  in  balsam.  The 
gastrocnemius  of  a  frog  is  convenient  on  account  of  its  small  size,  and  because  by 
bending  the  knee  over  and  tying  there,  the  muscle  can  be  easily  put  on  the  stretch 
and  kept  in  that  condition  during  fixation.  Place  the  entire  preparation  in  the 
fixative  removing  the  muscle-tendon  from  the  bone  after  fixation. 


CHAPTER  V. 

GLANDS  AND  THE  GENERAL  STRUCTURE  OF  MUCOUS 

MEMBRANES. 

Glands — General  Structure  and  Classification. 

Attention  was  called  in  describing  the  functional  activities  of 
cells  (page  46)  to  the  fact  that  certain  cells  possess  the  power  of  not 
only  carrying  on  the  nutritive  functions  necessary  to  maintain  their 
own  existence,  but  also  of  elaborating  certain  products  either  neces- 
sary for  the  general  body  functions  (secretions)  or  for  the  body  to 
eliminate  as  waste  (excretions).  Such  cells  are  known  as  gland  cells 
or  glandular  epithelium,  and  an  aggregation  of  these  cells  to  form  a 
definite  structure  for  the  purpose  of  carrying  on  secretion  or  excretion 
is  known  as  a  gland. 

A  gland  may  consist  of  a  single  cell,  as,  e.g.,  the  mucous  or  goblet 
cell  on  the  free  surface  of  a  mucous  membrane  or  the  unicellular  glands 
of  invertebrates.  Such  a  cell  undergoes  certain  changes  by  which  a 
portion  of  its  protoplasm  is  transformed  into  or  replaced  by  a  substance 
which  is  to  be  used  outside  the  cell  itself.  The  appearance  which  this 
cell  presents  depends  upon  the  stage  of  secretion.  It  is  thus  possible 
to  differentiate  between  a  "resting"  and  an  "active"  cell  or  between 
an  "empty"  and  a  "loaded"  cell.  The  mucous  secreting  cell  of  the 
intestine  is  one  of  the  simple  columnar  cells  which  constitute  the  epithe- 
lium of  the  mucous  membrane.  It  is  distinguishable  as  a  mucous 
or  goblet  cell  only  after  secretion  begins.  The  resting  cell  is  granular 
and  takes  a  rather  dark  cytoplasmic  stain.  As  the  cell  becomes  active, 
part  of  the  cytoplasm  is  transformed  into,  or  is  replaced  by,  a  clear  sub- 
stance which  does  not  stain  like  cytoplasm,  but  reacts  to  hgematoxylin. 
The  mucus  collects  first  in  the  free  end  of  the  cell,  and  gradually 
increases  in  amount  until  the  entire  cell  is  filled,  with  the  exception  of  a 
small  area  at  the  base,  where  a  little  unchanged  protoplasm  surrounds  a 
flattened  nucleus.  The  cell  at  this  stage  is  much  larger  than  in  the 
resting  state,  and  finally  ruptures  on  the  free  surface  and  pours  out  its 
secretion.  Opinions  differ  as  to  the  further  behavior  of  this  cell.  Ac- 
cording to  some,  its  life  history  is  now  ended,  and  its  place  is  taken  by 

186 


GLANDS.  187 

other  cells  which  pass  through  the  same  process.  This  undoubtedly 
takes  place  in  the  sebaceous  glands,  the  cells  of  which  disintegrate  to 
form  the  secretion.  Others  belie\-e  that  in  most  cases  the  cell  is 
reconstructed  from  the  nucleus  and  unchanged  cytoplasm,  and  again 
passes  through  the  process  of  secretion.  How  many  times  a  cell  may 
repeat  the  secretory  process  is  not  known.  In  stratified  epithelium 
secretion  may  begin  while  the  cell  is  still  deeply  situated,  but  is  com- 
pleted only  as  the  cell  reaches  the  surface,  where  its  mucus  is 
to   be   discharged. 

Most  glands  are  composed  of  more  than  one  cell,  usually  of  a  large 
number  of  cells,  and  these  cells,  instead  of  lying  directly  upon  the  sur- 
face, line  more  or  less  extensive  invaginations  into  which  they  pour 
their  secretions. 

In  the  simplest  form  of  glandular  invagination  all  the  cells  lining 
the  lumen  are  secreting  cells.  In  more  highly  developed  glands  only 
the  deeper  cells  secrete,  the  remainder  of  the  gland  serving  merely  to 
carry  the  secretion  to  the  surface.  This  latter  part  is  then  known  as 
the  excretory  duct,  in  contradistinction  to  the  deeper  secreting  portion. 
In  both  the  duct  portion  and  secreting  portion  of  a  gland  the  epithelium 
usually  rests  upon  a  more  or  less  definite  basement  membrane  or  mem- 
brana  propria  (page  63).  Beneath  the  basement  membrane,  separat- 
ing and  supporting  the  glandular  elements,  is  the  connective  tissue  of 
the  gland.  This  varies  greatly  in  structure  and  quantity  in  different 
glands. 

When  the  secreting  portion  of  the  gland  is  a  tubule,  the  lumen 
of  which  is  of  fairly  uniform  diameter,  the  gland  is  known  as  a  tubular 
gland.  When  the  lumen  of  the  secreting  portion  is  dilated  in  the 
form  of  a  sac  or  alveolus,  the  gland  is  known  as  a  saccular  or  alveolar 
gland.  Intermediate  forms  have  been  described  as  tubulo-alveolar 
glands. 

A  gland  may  consist  of  a  single  tubule  or  saccule,  or  of  a  single 
system  of  ducts  leading  to  terminal  tubules  or  saccules — simple  gland. 
A  gland  may  consist  of  a  number  of  more  or  less  elaborate  duct  systems 
with  their  terminal  tubules  or  saccules — compound  gland.  A  few  glands. 
e.g.,  the  thyreoid  and  thymus,  have  no  ducts,  and  arc  known  as  ductless 
glands. 

All  compound  glands  are  surrounded  by  connective  tissue  which 
forms  a  more  or  less  definite  capsule.  From  the  capsule  connective- 
tissue  septa  or  trabeculce  extend  into  the  gland.  The  broadest  septa 
usually  divide  the  gland  into  a  number  of  macroscopic  compartments 


188  THE  ORGANS. 

or  lobes.  Smaller  septa  from  the  capsule  and  from  the  interlobar 
septa  divide  the  lobes  into  smaller  compartments  usually  microscopic 
in  size — the  lobules.  A  lobule  is  not  only  a  definite  portion  of  the  gland 
separated  from  the  rest  of  the  gland  by  connective  tissue,  but  represents 
a  definite  grouping  of  tubules  or  alveoli  with  reference  to  one  or  more 
terminal  ducts.  The  glandular  (epithelial)  tissue  is  known  as  the 
parenchyma  of  the  gland,  in  contradistinction  to  the  connective  or 
interstitial  tissue. 

The  relations  of  the  glandular  tissue  proper  to  the  connective  tissue  are  best 
understood  by  reference  to  development.  All  glands,  simple  and  compound,  origi- 
nate as  simple  evaginations  from  a  surface  lined  with  epithelium.  The  epithelial 
evagination  grows  down  into  the  underlying  connective  tissue.  In  a.  compound 
gland  this  invagination  tubule  becomes  the  main  excretory  duct.  As  the  tubule 
grows,  it  divides  and  subdivides  to  form  the  larger  and  smaller  ducts  and  finally  the 
secreting  tubules  or  alveoli.  During  the  development  of  the  gland  tubules,  the  con- 
nective tissue  is  also  developing,  but  is  being  largely  replaced  by  the  mere  rapidly 
growing  tubules.  The  gland  tubules  do  not  develop  irregularly,  but  in  definite 
groups,  each  group  being  dependent  upon  the  tubule  (duct)  from  which  it  originates. 
Thus  the  invagination  tubule  (main  excretory  duct)  gives  rise  to  a  few  large  branches 
(lobar  ducts),  each  one  of  which  gives  off  the  subdivisions  which  constitute  a  lobe. 
From  each  lobar  duct  there  arise  within  the  lobe  a  large  number  of  smaller  branches 
(lobular  ducts)  each  one  of  which  gives  rise  to  the  subdivisions  included  in  a  lobule. 
As  the  lobe  groups  and  lobule  groups  of  tubules  develop,  the  largest  strands  of 
connective  tissue  are  left  between  adjacent  lobes  (interlobar  connective  tissue), 
smaller  strands  between  lobules  (interlobular  connective  tissue),  and  the  finest  con- 
nective tissue  between  the  tubules  or  alveoli  within  the  lobule  (intralobular  con- 
nective tissue). 

Glands  may  thus  be  classified  according  to  their  shape  and  ar- 
rangement as  follows: 

1.  Tubular  glands. 

i  straight. 

(a)  Simple  tubular  -^  coiled. 

'  branched. 

(b)  Compound  tubular. 

2.  Saccular  or  alveolar  glands. 

(a)  Simple  saccular. 

(b)  Compound  saccular  or  racemose. 

3.  Ductless  glands. 

J.  Tubular  Glands.  ~(a)  Simple  tubular  glands  are  simple 
tubules  which  open,  on  the  surface,  their  lining  epithelium  being  con- 
tinuous with  the  surface  epithelium.  All  the  cells  may  be  secreting 
cells  or  only  the  more  deeply  situated.     In  the  latter  case  the  upper 


GLANDS. 


189 


portion  of  the  tubule  serves  merely  as  a  duct.  In.  the  more  highly 
developed  of  the  simple  tubular  glands  we  distinguish  a  mouth,  opening 
upon  the  surface,  a  neck,  usually  somewhat  constricted,  and  a  fundus, 
or  deep  secreting  portion  of  the  gland. 

Simple  tubular- glands  are  divided  according  to  the  behavior  of 
the  fundus,  into  (i)  straight,  (2)  coiled,  and  (3)  branched. 

{1)  A  straight  tubular  gland  is  one  in  which  the  entire  tubule  runs 
a  straight  unb ranched  course,  e.g.,  the  glands  of  the  large  intestine 
(Fig.  113,  i). 

(2)  A  coiled  tubular  gland  is  one  in  which  the  deeper  portion  of 
the  tubule  is  coiled  or  convoluted,  e.g.,  the  sudoriferous  glands  of  the 
skin  (Fig.  113,  2). 


Fig.  113. — Diagram  Illustrating  Different  Forms  of  Glands.  Upper  row,  tubular 
glands;  i,  2,  and  3,  simple  tubular  glands;  4,  compound  tubular  gland.  Lower  row, 
alveolar  glands;  la,  2a,  and  ^a,  simple  alveolar  glands;  40,  compound  alveolar  gland.  For 
description  of  la,  2a,  and  3a,  see  simple  alveolar  glands  in  text. 


(3)  A  forked  or  branched  tubular  gland  is  a  simple  tubular  gland 
in  which  the  deeper  portion  of  the  tubule  branches,  the  several  branches 
being  lined  with  secreting  cells  and  opening  into  a  superficial  portion, 
which  serves  as  a  duct.  Examples  of  slightly  forked  glands  are  seen 
in  the  cardiac  end  of  the  stomach,  and  in  the  uterus.  Other  tubular 
glands  show  much  more  extensive  branching,  the  main  duct  giving 
rise  to  a  number  of  secondary  ducts,  from  which  are  given  oiT  the  termi- 
nal tubules.     The  mucous  glands  of  the  mouth,  oesophagus,  trachea. 


190  THE  ORGANS. 

and  bronchi  are  examples  of  these  more  elaborate  simple  tubular  glands 

(Fig.  113,  3)- 

(b)  Compound  tubular  glands  consist  of  a  number,  often  of  a 
large  number,  of  distinct  duct  systems.  These  open  into  a  common 
or  main  excretory  duct.  The  smaller  ducts  end  in  terminal  tubules. 
Many  of  the  largest  glands  of  the  body  are  of  this  type,  e.g.,  the  sali- 
vary glands,  liver,  kidney,  and  testis  (Fig.  113,  4). 

In  certain  compound  tubular  glands,  as,  e.g.,  the  liver,  extensive 
anastomoses  of  the  terminal  tubules  occur.  These  are  sometimes 
Called  reticular  glands. 

2.  Alveolar  Glands. — (a)  Simple  Alveolar  Glands. — The  sim- 
plest form  of  alveolar  gland  consists  of  a  single  sac  connected  with  the 
surface  by  a  constricted  portion,  the  neck,  the  whole  being  shaped  like 
a  flask  (Fig.  113,  i  a).  Such  glands  are  found  in  the  skin  of  certain 
amphibians;  they  do  not  occur  in  man.  Simple  alveolar  glands,  in 
which  there  are  several  saccules  (Fig.  113,  2  a),  are  represented  by  the 
smaller  sebaceous  glands.  Simple  branched  alveolar  glands,  in  which 
a  common  duct  gives  rise  to  a  number  of  saccules  (Fig.  113,  3  a),  are 
seen  in  the  larger  sebaceous  glands,  and  in  the  Meibomian  glands. 

{b)  Compound  Alveolar  Glands. — These  resemble  the  com- 
pound tubular  glands  in  general  structure,  consisting  of  a  large  num- 
ber of  duct  systems,  all  emptying  into  a  common  excretory  duct.  The 
main  duct  of  each  system  repeatedly  branches,  and  the  small  terminal 
ducts,  instead  of  ending  in  tubules  of  uniform  lumen,  as  in  a  tubular 
gland,  end  in  sac-like  dilatations,  the  alveoli  or  acini  (Fig.  113,  4  a). 
The  best  example  of  a  compound  alveolar  gland  is  the  mammary 
gland,  although  the  lung  is  constructed  on  the  principle  of  a  compound 
alveolar  gland. 

Certain  structures  remain  to  be  considered  which  are  properly 
classified  as  glands,  but  in  which  during  development  the  excretory 
duct  has  disappeared.     Such  glands  are  known  as  ductless  glands. 

The  ovary  is  a  ductless  gland,  the  specific  secretion  of  which,  the 
ovum,  is  under  normal  conditions  taken  up  by  the  oviduct  and  carried 
to  the  uterus.     This  is  known  as  a  dehiscent  gland. 

Other  ductless  glands,  such  as  the  thyreoid  and  adrenal,  are  known 
as  glands  of  internal  secretion,  their  specific  secretions  passing  directly 
into  the  blood  or  lymph  systems. 

A  few  glands,  e.g.,  the  liver  and  pancreas,  have  both  an  internal 
secretion,  and  an  external  secretion. 


GENERAL  STRUCTURE  OF  MUCOUS  MEMBRANES.  191 

General  Structure  of  Mucous  Membranes. 

The  alimentary  tract,  the  respiratory  tubules,  parts  of  the  genito- 
urinary system,  and  some  of  the  organs  of  special  sense  are  lined  by 
mucous  membranes.  While  differing  as  to  details  in  different  organs, 
the  general  structure  of  all  mucous  membranes  is  similar.  The  essen- 
tial parts  are  (i)  surface  epithelium,  (2)  basement  membrane,  and 
(3)  stroma  or  tunica  propria.  The  epithelium  may  be  simple  colum- 
nar, as  in  the  gastro-intestinal  canal;  ciliated,  as  in  the  bronchi; 
stratified  squamous,  as  in  the  oesophagus,  etc.  The  epithelium  rests 
upon  a  basement  membrane  or  membrana  propria  which,  like  the  same 
membrane  in  glands,  is  described  by  some  as  a  product  of  the  epithe- 
lium, by  others  as  a  modification  of  the  underlying  connective  tissue. 
Beneath  the  basement  membrane  is  a  connective-tissue  stroma,  or 
tunica  propria.  This  usually  consists  of  loosely  arranged  fibrous 
tissue  with  some  elastic  fibres.  It  may  contain  smooth  muscle  cells 
and  lymphoid  tissue. 

In  addition  to  the  three  layers  above  described  there  is  frequently 
a  fourth  layer  between  the  stroma  and  the  underlying  connective  tissue. 
This  consists  of  one  or  more  layers  of  smooth  muscle,  and  is  known  as 
the  muscularis  mucosce. 

A  mucous  membrane  usually  rests  upon  a  layer  of  connective 
tissue  rich  in  blood-vessels,  lymphatics,  and  nerves — the  siibmucosa. 


CHAPTER  VI. 
THE  DIGESTIVE  SYSTEM. 

The  digestive  system  consists  of  the  alimentary  tract  and  certain 
associated  structures  such  as  glands,  teeth,  etc. 

The  alimentary  tract  is  a  tube  extending  from  lips  to  anus.  Dif- 
ferent parts  of  the  tube  present  modifications  both  as  to  calibre  and  as 
to  structure  of  wall. 

The  embryological  subdivision  of  the  canal  into  headgut,  foregut, 
midgut,  and  endgut  admits  of  further  subdivision  upon  an  anatomical 
basis  as  follow^s: 

I.  Headgut:  (a)  Mouth,  including  the  tongue  and  teeth. 

{h)  Pharynx. 

II.  Foregut:    {a)  CEsophagus. 

{h)  Stomach. 

III.  Midgut:  Small  intestine. 

IV.  Endgut:    {a)  Large  intestine. 

{h)  Rectum. 

The  entire  canal  is  lined  by  mucous  membrane,  the  modifications 
of  which  constitute  the  most  essential  difference  in  structure  of  its 
several  subdivisions. 

Beneath  the  mucosa  is  usually  more  or  less  connective  tissue,  which 
in  a  large  portion  of  the  canal  forms  a  definite  suhmucosa. 

Muscular  tissue  is  present  beneath  the  submucosa  throughout  the 
greater  part  of  the  canal.  In  most  regions  it  forms  a  definite,  con- 
tinuous, muscular  tunic. 

The  upper  and  lower  ends  of  the  tube — mouth,  pharynx,  oesoph- 
agus, and  rectum — are  quite  firmly  attached  by  fibrous  tissue  to  the 
surrounding  structures.  The  remainder  of  the  tube  is  less  firmly 
attached,  lying  coiled  in  the  abdominal  cavity,  its  surface  covered, 
except  along  its  attached  border,  by  a  serous  membrane,  the  visceral 
peritoneum. 

192 


THE  DIGESTIVE  SYSTEM.  193 

I.  THE  HEADGUT. 

The  Mouth. 

The  Mucous  Membrane  of  the  Mouth.— This  consists  of 
stratified  squamous  epithelium  lying  upon  a  connective-tissue  stroma 
or  tunica  propria.  The  latter  is  thrown  up  into  papilla,  which  do 
not,  however,  appear  upon  the  free  surface  of  the  epithehum.  The 
submucosa  is  a  firm  connective-tissue  layer  with  few  elastic  fibres. 
The  thickness  of  the  epithehum,  the  character  of  the  stroma,  and  the 
height  of  the  papillae  vary  in  different  parts  of  the  mouth.  There  is 
no  muscularis  mucosas. 

x\t  the  junction  of  the  skin  and  mucous  membrane  (red  margin  of 
the  lips)  the  epithelial  layer  is  much  thickened,  the  stroma  is  thinned, 
and  the  papillae  are  very  high.  At  this  point  the  stratum  corneum 
of  the  skin  passes  over  into  the  softer  nucleated  epithehum  of  the 
mouth,  while  the  stratum  lucidum  and  stratum  granulosum  of  the 
skin  terminate  (see  skin,  page  354). 

The  mucous  membrane  of  the  gums  has  prominent,  long,  slender 
papillae,  the  summits  of  which  are  covered  by  a  very  thin  layer  of 
epithelium.  This  nearness  of  the  vascular  stroma  to  the  surface 
accounts  for  the  ease  with  which  the  gums  bleed.  That  portion  of 
the  gums  which  extends  over  the  teeth  is  devoid  of  papillae.  The 
submucosa  of  the  gums  is  firmly  attached  to  the  underlying  periosteum. 

The  mucous  membrane  lining  the  cheeks  has  low,  small  papillae, 
and  the  submucosa  is  closely  adherent  to  the  muscular  fibres  of  the 
buccinator. 

Covering  the  hard  palate,  the  mucous  membrane  is  thin  and  the 
short  papillae  are  obliquely  placed,  their  apices  being  directed  ante- 
riorly.    The  submucosa  is  firmly  attached  to  the  periosteum. 

Over  the  soft  palate  the  papillae  of  the  mucous  membrane  are  low 
or  even  absent.  They  are  somewhat  higher  on  the  uvula,  the  poste- 
rior surface  of  which  shows  a  transitional  condition  of  its  epithe- 
lium, areas  of  stratified  squamous  alternating  with  areas  of  stratified 
columnar  ciliated  epithelium.  Throughout  the  mucous  membrane  of 
the  soft  palate,  u\ula,  and  fauces,  the  stroma  and  submucosa  contain 
diffuse  lymphatic  tissue.  In  some  places  the  lymphoid  cells  are  so 
closely  placed  as  to  form  distinct  nodules. 

Glands  of  the  Oral  Mucosa.^ — Distributed  throughout  the 
oral  mucosa  are  small  l^ranched  tul)ular  glands.      Only  in  those  parts 

'  For  description  of  the  larger  salivary  glands  see  page  242. 


194  THE  ORGANS. 

of  the  mucous  membrane  which  are  closely  attached  to  underlying 
bone,  as  on  the  gums  and  hard  palate,  are  mucous  glands  few  or 
entirely  absent.  While  the  deeper  portions  of  the  glands  are  in  the 
submucosa,  some  of  the  tubules  usually  lie  in  the  stroma  of  the  mu- 
cous membrane. 

The  ducts  open  upon  the  surface  and  are  lined  with  a  continuation 
of  the  surface  stratified  squamous  epithelium  as  far  as  the  first  bifur- 
cation. Here  the  epithelium  becomes  stratified  columnar,  and  this, 
as  the  smaller  branches  are  approached,  passes  over  into  the  simple 
columnar  type.  Not  infrequently  ducts  of  small  secondary  glands 
empty  into  the  main  duct  during  its  passage  through  the  mucosa. 

According  to  the  character  of  their  secretions,  the  oral  glands  are 
divided  into: 

{a)  Mucous  glands,  which  secrete  a  mucin-containing  fluid  (mucus) ; 

(b)  Serous  glands,  which  secrete  a  serous  (albuminous)  fluid; 

(c)  Mixed  glands,  the  secretion  of  which  is  partly  mucous  and 
partly  serous. 

Morphologically,  also,  a  similar  distinction  can  be  made  in  regard 
to  the  glandular  epithelium  which  lines  the  terminal  tubules,  the 
tubules  of  mucous  glands  being  lined  with  "mucous"  cells,  those  of 
serous  glands  with  "serous  cells,"  while  of  the  mixed  glands  the  cells 
of  some  tubules  are  mucous,  of  others  serous.  In  certain  tubules 
both  mucous  and  serous  cells  occur.  The  appearance  which  these 
cells  present  depends  largely  upon  their  secretory  condition  at  the  time 
of  death. 

Serous  cells  when  resting  have  a  slightly  granular  protoplasm, 
which  in  the  fresh  condition  is  highly  refractive,  giving  the  cells  a 
transparent  appearance.  With  the  beginning  of  secretion  the  granules 
increase  in  number  and  the  cells  become  darker.  Stained  with 
hsematoxylin-eosin,  serous  tubules  have  a  purplish  color.  The  nuclei 
are  spherical  or  oval,  and  are  situated  between  the  centre  and  base 
of  the  cell  (Fig.  159,  p.  245). 

Mucous  cells  are  in  the  quiescent  state  rather  small  cuboidal  or 
pyramidal  cells,  with  cloudy  cytoplasm  and  nuclei  situated  at  the  base 
of  the  cell.  When  active  the  mucous  cells  are  much  larger,  with  clear 
cytoplasm  and  with  nuclei  flattened  against  the  basement  membrane. 
The  protoplasm  of  the  fresh  unstained  mucous  cell  is  less  highly 
refractive  than  that  of  the  serous  cell.  It  consequently  appears  darker 
and  less  transparent.  Mucous  tubules  are  larger  and  more  irregular 
in  shape  than  serous  tubules,  and  when  stained  with  hsematoxylin-eosin 


THE  DIGESTIVE  SYSTEM.  195 

either  remain  almost  wliolly  unstained  or  take  a  pale  blue  haematoxylin 
stain  (Fig.  159,  p.  245).  Many  mucous  tubules  have  in  addition  to  the 
mucous  cells  a  peculiar,  often  crescentic-shaped  group  of  cells  on  one 
side  of  the  tubule,  between  the  mucous  cells  and  the  basement  mem- 
brane. These  cells  are  granular  and  stain  very  much  like  serous  cells 
with  haematoxylin-eosin,  thus  resembhng  the  latter  in  appearance. 
On  account  of  the  shape  of  the  groups,  they  are  known  as  the  crescents 
of  Gianuzzi  or  demilunes  of  Heidenhain  (Fig.  159,  p.  245).  The  cells 
of  the  crescents  are  connected  with  the  lumen  by  means  of  secretory 
canals,  which  pass  between  the  mucous  cells  and  end  in  branches  within 
the  protoplasm  of  the  crescent  cells.  It  is  quite  possible  that  some  of 
the  crescents  are  not  serous  cells  but  mucous  cells  in  the  non-active 
condition  which  have  been  pushed  away  from  the  lumen  by  the  more 
active  cells.  Such  cell  groups  are  not  connected  with  the  lumen  of  the 
gland  by  intercellular  secretory  canals. 

Peculiar  irregular  branching  cells  have  been  described,  extending 
from  the  basement  membrane  in  between  the  mucous  cells.  They 
are  known  as  "basket"  cells  and  are  supposed  to  be  supportive  in 
character. 

The  cells  of  both  mucous  and  serous  tubules  rest  upon  a  membrana 
propria,  outside  of  which,  separating  the  tubules,  is  a  cellular  connect- 
ive-tissue stroma. 

Of  the  small  glands  of  the  mouth,  a  group  near  the  root  of  the 
tongue  are  of  the  mucous  variety,  some  "lingual"  glands  in  the  region 
of  the  circumvallate  papillae  are  serous,  while  the  remainder  are  of  the 
mixed  type. 

Blood-vessels. — The  larger  vessels  run  mainly  in  the  submucosa. 
The  arteries  of  the  submucosa  give  off  one  group  of  branches  to  the 
tunica  propria,  where  they  break  up  into  a  dense  subepithelial  capillary 
network,  sending  capillary  loops  into  the  papillae.  A  second  group 
of  arterial  branches  pass  to  the  submucosa,  where  they  give  rise  to 
capillary  networks  among  the  tubules  of  the  mucous  glands.  From 
the  capillaries  veins  arise  which  accompany  the  arteries. 

Lymphatics. — The  larger  lymph  vessels  lie  in  the  submucosa. 
These  send  smaller  branches  into  the  tunica  propria,  where  they  open 
into  small  lymph  capillaries  and  spaces. 

Nerves. — Medullated  nerve  fibres  form  plexuses  in  the  submucosa 
and  deeper  parts  of  the  mucosa.  From  these  plexuses,  branches  are 
given  off  which  lose  their  medullary  sheaths  and  form  a  second 
plexus  of  non-medullated  filires  just  Ijeneath  the  epithelium.     From 


196  THE  ORGANS. 

this  subepithelial  plexus,  branches  pass  in  between  the  epithelial 
cells  to  terminate  in  end  brushes  or  in  tactile  corpuscles.  The 
nerves  belong  to  the  cerebro-spinal  system,  and  are  dendrites  of 
sensory  ganglion  cells.  Axones  of  sympathetic  neurones  are  also 
present  in  the  oral  mucosa,  destined  mainly  for  the  muscle-tissue  of 
the  blood-vessels. 

TECHNIC. 

(i)  The  superficial  cells  of  the  oral  mucous  membrane  may  be  prepared  for 
examination  as  in  technic  i,  page  57. 

(2)  For  the  study  of  the  mucous  membrane  of  different  parts  of  the  mouth,  fix 
small  pieces  in  formalin-Miiller's  fluid  (technic  5,  p.  7),  cut  sections  perpendicular 
to  the  surface,  stain  with  haematoxylin-eosin  (technic  i,  p.  18),  and  mount  in  balsam. 

(3)  Small  mucous  and  serous  glands  of  the  mouth  may  be  studied  in  the  pre- 
ceding sections. 

The  Tongue. 

The  tongue  is  composed  mainly  of  striated  muscle  fibres,  supported 
by  connective  tissue  and  covered  by  a  mucous  membrane.     While  the 


Fungiform 
papillae 


Fig.  114. — Surface  View  of  Tongue  showing  filiform  papilla: 
and  three  fungiform  papillae  (Spalteholz). 

bundles  of  fibres  interlace  in  all  directions,  three  fairly  distinct  planes 
can  be  differentiated. 

(i)  Vertical  and  somewhat  radiating  fibres — hyoglossus,  genio- 
glossus,  and  vertical  fibres  of  the  lingualis. 

(2)  Transverse  fibres — transverse  fibres  of  the  lingualis. 


THE  DIGESTIVE  SYSTEM. 


197 


(3)  Longitudinal  j&bres — the  styloglossus  and  longitudinal  (superior 
and  inferior)  fibres  of  the  lingualis. 

The  connective  tissue  which  supports  the  muscle  fibres  and  sepa- 
rates them  into  bundles  contains  mucous  glands  and  fat.  A  strong 
band  of  connective  tissue,  the  septum  lingucF,  extends  lengthwise 
through  the  middle  of  the  tongue,  dividing  it  into  right  and  left  halves. 

The  suhmucosa  of  the  tongue  is  not  well  developed,  the  stroma  of 
the  mucosa  resting  directly  upon  the  underlying  muscle. 


£'.-M5  V  ,;>•:;/•  ^}. 


Fig.  115. — ^Vertical  Section  through  Two  Filiform  Papillte  from  Human  Tongue. 
X  80.  (Szymonowicz.)  a,  Horny  epithelium;  h,  stroma;  c,  epithelium;  d,  secondary 
papilla. 


The  mucous  membrane  of  the  tongue  resembles  that  of  the  mouth, 
but  differs  from  the  latter  in  that  in  addition  to  the  low  papillae,  such 
as  are  found  in  the  oral  mucosa,  the  upper  surface  of  the  tongue  is 
studded  with  numerous  and  much  larger  papillae  or  villi.  These  pro- 
ject from  the  surface  and  give  to  the  tongue  its  characteristic  roughness. 
Three  forms  of  papillae  are  distinguished.  Filiform,  fungiform,  and 
circumvallate. 

(i)  Filiform  Papill.e  (Fig.  115). — These  are  the  most  numerous 
and  are  distributed  over  the  entire  dorsum  of  the  organ.  Each  con- 
sists of  a  central  core  of  conncctixe  tissue  containing  ehistic  fibres, 


198 


THE  ORGANS. 


which  is  long  and  slender,  and  is  covered  by  stratified  squamous 
epitheHum.  From  the  summit  of  each  papilla  are  given  off  several 
secondary  papilla.  The  epithelium  covering  the  papillae  is  hornified 
and  often  extends  from  the  surface  as  a  long  thread-like  projection — 
hence  the  name,  filiform. 

(2)  Fungiform  Papilla  (Fig.  116). — Scattered  irregularly  over 
the  entire  dorsum  among  the  filiform  papillae,  but  fewer  in  number, 
are  larger  papillae  of  somewhat  different  structure  known  as  fungiform 
papillae.     Their  summits  are  rounded  instead  of  pointed  and  their 


m- 


Fig.  116. — Vertical  Section  through  Fungiform  Papilla  of  Human  Tongue.      X  45.     (Szy- 
monowicz.)     a,  Secondary  papilla;  b,  epithelium;  c,  muscle  fibres. 


bases  are  narrowed.  Secondary  papillae  are  given  off  not  only  from 
the  summit,  but  from  the  sides  of  the  papilla.  The  epithelial  cov- 
ering is  comparatively  thin  and  is  not  hornified.  The  connective- 
tissue  core  of  these  papillae  contains  but  few  elastic  fibres. 

(3)  The  Circumvallate  Papilla  (Fig.  117). — These  are  from 
nine  to  fifteen  in  number,  and  are  grouped  on  the  posterior  surface 
of  the  dorsum  of  the  tongue.  They  resemble  the  fungiform  papillae, 
but  are  much  larger.  Each  lies  rather  deep  in  the  mucous  membrane, 
surrounded  by  a  groove  or  trench  and  wall  (whence  the  name  circum- 
vallate). The  wall  is  somewhat  lower  than  the  papilla,  thus  allowing 
the  latter  to  project  slightly  above  the  surface.     Secondary  papillae 


THE  DIGESTIVE  SYSTEM. 


199 


are  confined  to  the  upper  surface  of  the  papilla,  the  sides  being  free 
from  secondary  papillae.  The  surface  of  the  papilla  and  the  borders 
of  the  groove  and  wall  are  covered  by  stratified  squamous  epithelium. 
Lying  in  the  epithelium  of  the  side  wall  and  sometimes  of  the  opposite 
trench  wall  are  oval  bodies,  the  so-called  taste  buds,  which  serve  as 
organs  for  the  nerves  of  taste  (see  nervous  system).  Into  the  trench 
surrounding  the  circumvallate  papilla  open  the  ducts  of  serous  glands 
(Ebner's  glands). 


ar(\c^ 


Fig.  117. — ^\"ertical  Section  through  a  Circumvallate  Papilla  of  Human  Tongue. 
X  37.  (Szymonowicz.)  a,  Secondary  papilla;  b,  wall;  c,  trench;  d,  epithelium  of  tongue; 
e.  stroma;  /,  submucosa;  g,  Ebner's  glands. 


The  lymph  follicles  of  the  tongue  have  been  already  described 
(page  157)  under  the  head  of  the  lingual  tonsils. 

For  glands  of  the  tongue  see  page  195. 

The  larger  blood-vessels  run  in  the  connective-tissue  septa. 
These  give  off  smaller  branches,  which  break  up  into  capillary  net- 
works surrounding  the  muscle  fibres  and  forming  a  ple.xus  just  be- 
neath the  epithelium.  From  the  latter  are  given  oft"  capillaries  to 
the  papillae.  The  capillaries  converge  to  form  veins,  which  in  general 
follow  the  course  of  the  arteries. 

Fine  lymph  spaces  occur  in  the  papillae  and  open  into  a  plexus  of 
small  lymph  capillaries  just  beneath  the  papilla?.     These  communi- 


200  THE  ORGANS. 

cate  with  a  deeper  plexus  of  larger  lymphatics,  which  increase  in  size 
and  number  as  they  pass  backward  and  form  an  especially  dense 
lymphatic  network  at  the  root  of  the  tongue  in  the  region  of  the 
lingual  tonsils. 

Nerves. — Sympathetic  fibres  pass  mainly  to  the  smooth  muscle 
of  the  blood-vessels  and  to  the  glands.  Medullated  motor  nerve 
fibres  supply  the  lingual  muscles.  Medullated  sensory  nerves  in- 
clude those  of  the  special  sense  of  taste  as  well  as  those  of  ordi- 
nary sensation.  They  end  freely  among  the  epithelial  cells  or  in 
connection  with  special  end-organs — the  taste  buds  mainly  in  the 
circumvallate  papillae,  and  the  end-bulbs  of  Krause  in  the  fungiform 
papillae. 

TECHNIC. 

Remove  pieces  of  the  dorsum  of  ihe  tongue,  selecting  parts  that  will  include 
the  dififerent  forms  of  papillae  and  cutting  well  into  the  underlying  muscular  tissue. 
Treat  as  in  technic  2,  p.  ig6,  or  sections  may  be  stained  with  hsematoxylin-picro- 
acid-fuchsin  (technic  3,  p.  19). 

In  sections  from  the  back  part  of  the  tongue  good  examples  of  mucous  and 
serous  glands  are  usually  found. 

In  small  sections  of  the  tongue  the  muscle  fibres  are  seen  arranged  in  bundles, 
surrounded  by  connective  tissue  and  interlacing  in  all  directions.  For  the  study  of 
the  arrangement  of  the  different  planes  of  muscle,  complete  transverse  sections 
should  be  made  at  intervals  through  the  entire  tongue.  The  muscle  and  connective- 
tissue  relations  are  best  brought  out  by  the  haematoxylin-picro-acid-fuchsin  stain. 

The  Teeth. 

A  tooth  is  a  hard  bone-like  structure,  part  of  which  projects  above 
the  surface  of  the  jaw  as  the  crown,  while  the  deeper  portion,  the  root 
or  fang,  is  buried  in  a  socket  of  the  alveolar  margin  (Fig.  118).  The 
junction  of  the  root  and  crown  is  known  as  the  neck. 

A  tooth  consists  of  a  soft  central  core,  the  pulp  cavity,  surrounded 
by  dentine  (Figs.  118  and  119).  The  latter  constitutes  the  main  bulk 
of  the  tooth.  The  exposed  portion  of  the  dentine  is  covered  by  a  thin 
layer  of  extremely  hard  substance,  the  enamel  (Fig.  118,  i),  while  the 
alveolar  portion  of  the  dentine  is  covered  with  cementum  (Fig.  118,  3). 
Of  these  the  dentine  and  cementum  are  of  connective-tissue  origin, 
the  enamel  of  epithelial. 

The  pulp  cavity  occuyjies  the  central  axis  of  the  tooth  (Figs.  118  and 
119).     In  the  root  it  is  known  as  the  root  canal.     At  the  apex  of  the 


THE  DIGESTR'E  SYSTEM. 


201 


root  it  communicates  with  the  underlying  tissue  by  means  of  a  minute 
opening,  through  which  blood-vessels  and  nerves  enter  the  pulp  cavity. 

The  dentinal  pulp  consists  of  loose  connective  tissue  of  an  embryonal 
type,  composed  of  many  fusiform  and  stellate  cells  and  comparatively 
dehcate  fibrils  not  joined  to  form  bundles.  The  pulp  is  richly  supplied 
with  blood-vessels  and  nerves  wdiich  are 
found  only  in  this  part  of  the  tooth. 
Along  the  dentinal  surface  of  the  pulp 
the  connective  tissue  cells  are  arranged 
as  a  single  layer  of  columnar  cells,  the 
odontoblasts.  These  cells  are  closely 
allied  to  osteoblasts.  Their  nuclei  lie 
toward  their  inner  ends.  Each  cell 
sends  out  an  inner  process,  which  is 
usually  single  and  passes  into  the  den- 
tinal pulp,  several  lateral  processes 
which  interlace  with  and  probably 
anastomose  with  similar  processes  from 
other  cells,  and  one  or  more  outer  fibre- 
like processes  which  enter  the  dentine, 
where  they  form  the  dentinal  fibres. 
These  frequently  extend  entirely  through 
the  dentine. 

Dentine  (Figs.  119  and  120,  D)  is 
somewhat  harder  than  bone   which   it 
resembles  in  structure.      According  to  Fig.  nS. 
von  Bibra  its  chemical  composition  is: 


Organic  matter,  28.01 

Calcium  phosphate  and  fluorid,  66.  72 

Calcium  carbonate,  3-36 

Magnesium  phosphate,  i .  18 

Other  salts,  o-73 


Vertical  Section  of  Tooth  hi 
situ.  X  15.  (Waldeyer.)  c,  Pulp 
cavity,  the  letter  being  at  about  the 
junction  of  crown  and  root;  i, 
enamel  showing  radial  and  longi- 
tudinal markings;  2,  dentine  showing 
dental  canals;  3,  cementum  (con- 
taining bone  corpuscles);  4,  dental 
periosteum;  5,  bone  of  lower  jaw. 


Dentine  constitutes  the  bulk  of  the  tooth  and  is  peculiar  in  that  it 
contains  canaliculi,  dental  canals  (Figs.  119  and  120,  Dk).  but  no 
lacunas  or  bone  cells.  The  latter  are  represented  by  the  odontoblasts 
of  the  pulp,  which,  as  already  noted,  lie  at  the  inner  side  of  the  dentine, 
into  the  canaliculi  of  which  they  send  the  dentinal  fibres.  Dentine  is 
non-vascular.  The  dental  canals  begin  at  the  dental  pulp,  where  they 
have  a  calibre  of  2  to  5/!.  They  pass  outward  radially,  taking  a 
somewhat  cur\-ed  course,  to  the  limit  of  the  dentine,  and,  while  taking 


202  THE  ORGANS. 

different  directions  in  different  parts  of  the  dentine,  are  essentially 
parallel.  In  a  longitudinal  section  of  the  dentine  of  the  crown,  lines 
are  seen  running  parallel  to  the  surface  of  the  tooth.  They  are  known 
as  the  incremental  lines  of  Schreger.  They  are  apparently  due  to 
regularity  of  curvature  in  the  dental  tubules.  In  their  passage  through 
the  dentine  the  main  canals  gradually  grow  smaller  until  their  diameter 


K 


'  jt  »  *  ^  ^       •^~      *•- 


',*  -•.'''' 


::?ifi 


«  *  ■ 


''"  >X,^„i<"'" 


,J' 


!''.'. 


^  l»f-'v'^''Z   .*' 


Fig.  iig. — Cross  Section  through  Root  of  Human  Canine  Tooth  (X  25)  (Sobotta), 
showing  relations  of  pulp  cavity,  dentine,  and  cementum.  P,  Pulp  cavity;  D,  dentine; 
C,  cementum;  A',  Tomes'  granular  layer. 

is  from  0.5  to  1/7.  They  give  off  minute  side  branches  from  0.3  to 
0.6/j!  in  diameter,  which  leave  the  main  tubules  at  almost  right  angles, 
but  soon  turn  slightly  outward.  They  anastomose  with  similar 
branches  from  other  canals.  This  anastomosis  takes  place  not  only 
between  branches  of  adjacent  canals,  but  also  between  branches  of 
canals  some  distance  apart.  The  main  canals  terminate  either  in 
blind  extremities,  or  form  loops  by  anastomosing  with  neighboring 


THE  DIGESTR'E  SYSTEM. 


203 


tubules.  Some  of  the  tubules  have  quite  extensive  terminal 
branchings,  other  tubules  have  only  two  or  three  end  branches.  A 
few  tubules  run  slightly  beyond  the  limits  of  the  dentine  into  the  enamel. 
They  do  not  pass  into  the  cementum.  The  arrangement  of  the  dental 
canals  and  their  branches  differs  in  dift"erent  parts  of  the  tooth.  In  the 
crown  there  are  few  large  branches  and  the  main  canals  are  quite 
straight,  most  of  them  ending  blindly  in  brush-like  branchings  just 
under  the  enamel,  but  some  continuing  over  into  the  enamel  for  from 
lo  to  4.o/(,  where  they  lie   in  the  cement   betw^een  the  prisms.     In 


KH 


Dk 


Fig.  1 20. — From  Longitudinal  Section  through  Root  of  Human  jSIolar  Tooth  ( X  200) 
(Sobotta),  showing  junction  of  dentine  and  cementum.  C,  Cementum;  D,  dentine;  K, 
Tomes'  granular  layer;  Dk,  dental  canals;  KH,  lacunae  of  cementum. 


the  root  the  canals  have  more  large  branches  and  are  more  uneven. 
They  do  not  pass  over  into  the  cementum,  but  end  at  the  granular  layer. 
The  dentine  immediately  around  a  dental  canal  is  more  dense  and  hard 
than  elsewhere  and  forms  a  sort  of  sheath  for  the  canal — Neumann^ s 
dental  sheath.  Between  the  dental  canals  is  a  calcified  ground  sub- 
stance, in  which  are  connective-tissue  fibres  running  in  the  long  a.xis 
of  the  tooth. 

Spaces  which  probably  represent  incomplete  calcification  of  the 
dentine  occur  in  the  peripheral  portion  of  the  dentine  of  the  crown. 
These  are  known  as  interglobular  spaces  (Fig.  121,  Jg).  They  are  filled 
with  a  substance  resemblinc:  uncalcified  dentine.     The  interglobular 


204  THE  ORGANS. 

spaces  do  not  interrupt  the  dental  canals  which  pass  through  them 
with  no  break  in  their  continuity. 

In  the  outer  part  of  the  dentine  of  the  root  are  similar  spaces 
which  are  smaller  and  more  closely  placed.  These  form  the  so-called 
Tomes'  granular  layer  (Fig.  120,  A').  In  the  root  of  the  tooth  this 
layer  is  quite  thick,  separating  the  cementum  from  the  dentine.  Its 
spaces  or  lacunae  send  off  tiny  canaliculi  which  run  in  all  directions  and 
anastomose  with  one  another,  with  the  dentinal  tubules,  and  with  the 
lacunae  of  the  cementum.  This  layer,  with  its  small  closely  placed 
spaces  and  fine  irregularly  running  canaliculi,  contrasts  sharply  on  the 
one  side  (Fig.  120)  with  the  dentine  and  its  straight  parallel  tubules; 
and  on  the  other  side,  with  the  cementum  and  its  large  and  more 
widely  separated  lacunae.  Over  the  crown  of  the  tooth  this  layer  is 
much  thinner  and  as  the  apex  is  approached,  becomes  lost  completely,, 
the  dental  tubules  extending  to,  and  some  of  them  entering  slightly, 
(see  above)  the  enamel. 

The  ENAMEL  covers  the  exposed  part  or  crown  of  the  tooth  and  is 
the  hardest  substance  in  the  body.  It  contains  little  more  than  a  trace 
of  organic  substance,  its  chemical  composition  being,  according  to  von 
Bibra : 

Organic  matter,  3 .  59 

Calcium  phosphate  and  fluorid,  89.82 

Calcium  carbonate,  4-37 

Magnesium  phosphate,  i-34 

Other  salts,  0.88 

It  consists  of  long  six-sided  prisms  3  to  6//.  in  diameter — enamel  fibres 
or  enamel  prisms  (Fig.  121,  Sp) — which  take  a  slightly  wavy  course 
through  the  entire  thickness  of  the  enamel.  The  prisms  are  at- 
tached to  one  another  by  a  small  amount  of  cement  substance,  and  are 
grouped  into  bundles,  the  prisms  of  each  bundle  being  parallel,  but  the 
bundles  themselves  frequently  crossing  one  another  at  acute  angles.  In 
the  human  adult  the  prisms  are  homogeneous;  in  the  embryo  they  show 
a  longitudinal  fibrillation.  Rather  indistinct  parallel  lines  (the  lines  of 
Retzius)  cross  the  enamel  prisms.  They  probably  represent  the  de- 
position in  layers  of  the  lime  salts,  although  they  are  considered  by 
some  as  artefacts.  The  enamel  is  covered  by  an  apparently  structure- 
less membrane,  the  culicula  dentis. 

The  CEMENTUM  (Fig.  120,  C)  covers  the  dentine  of  the  root  in  a 
manner  similar  to  that  in  which  the  enamel  covers  the  dentine  of  the 
crown  (Fig.  118,  i  and  3).     It  forms  a  thin  layer  at  the  neck,  but  in- 


THE  DIGESTR'E  SYSTEM. 


205 


creases  in  thickness  as  the  deeper  part  of  the  root  is  reached.  Cemen- 
tum  is  bone  tissue.  It  contains  lacunce  and  boiie  cells.  From  the 
lacunae  radiate  canaHcuH.  but  there  is  no  distinct  lamellation  and  no 
Haversian  systems  or  blood-vessels,  excepting  in  the  large  teeth  of  the 
larger  mammalia,  and  in  the  teeth  of  the  aged,  where  they  may  be 
present.  Channels,  similar  to  \'olkmann's  canals  in  bone,  not  sur- 
rounded by  concentric  lamellae,  but  serving  for  the  passage  of  blood- 
vessels, are  quite  frequent  in  the  thicker  portions  of  the  cementum. 


Sr 


Dk 


■k 


S 

Fig.  121. — From  Longitudinal  Section  of  Crown  of  Human  Premolar  (X  2co) 
(Sobotta),  showing  junction  of  enamel  and  dentine.  5,  Enamel;  Z?,  dentine;  5/),  enamel 
prisms;  Dk,  dental  canals;  Jg,  interglobular  spaces.  A  few  dentinal  fibres  are  seen  passing 
beyond  the  limits  of  the  dentine  into  the  enamel.  The  oblique  dark  bands  in  the  enamel 
are  the  lines  of  Retzius. 


The  ground  substance  of  the  cementum  is  continuous  with  that  of 
the  dentine  and  many  canaliculi  of  the  former  open  into  the  interglob- 
ular spaces  of  the  latter.  Many  uncalcified  Sharpey's  fibres  penetrate 
the  cementum. 

The  union  between  the  root  of  the  tooth  and  the  alveolar  peri- 
osteum is  accomplished  by  a  reflection  of  the  latter  over  the  root, 
where  it  forms  the  dental  periosteum,  or  peridental  membrane  (Fig. 
ii8,  4).  This  membrane  consists  of  dense  fibrous  connecti\"e  tissue. 
At  the  neck  of  the  tooth  it  l)lcnds  with  the  submucosa  of  the  gum  to 
form  the  so-called  circular  dcntoid  lii^auu'iil.  an  annular  band  of  dense 


206  THE  ORGANS. 

fibrous  tissue,  which  extends  around  the  tooth.  The  peridental  mem- 
brane is  formed  of  fibrillar  connective  tissue  free  from  elastic  fibres. 
Its  fibres  are  directly  continuous  with  Sharpey's  fibres  of  the 
cementum. 

Blood-vessels  of  teeth  are  confined  entirely  to  the  pulp  cavity. 
One  or  two  small  arteries  reach  the  pulp  cavity  from  the  underlying 
connective  tissue,  through  the  foramen  in  the  apex  of  the  root.  These 
break  up  into  a  capillary  network  in  the  dental  pulp. 

Lymphatics  have  as  yet  not  been  demonstrated  in  the  dental  pulp. 

Nerves. — Medullated  fibres  accompany  the  blood-vessels  through  the 
apical  canal.  In  the  pulp  they  break  up  into  a  number  of  non-medul- 
lated  branches,  which  form  a  plexus  along  the  outer  edge  of  the  pulp, 
beneath  the  odontoblasts.  From  this  plexus  branches  are  given  off 
which  pass  in  between  the  odontoblasts,  some  terminating  there, 
while  others  end  between  the  odontoblasts  and  the  dentine. 

Development. — The  enamel  of  the  teeth  is  of  ectodermic  origin, 
the  remainder  of  mesodermic.  The  earliest  indication  of  tooth  forma- 
tion occurs  about  the  seventh  week  of  intra-uterine  life  (embryos 
12  to  15  mm.).  It  consists  in  a  dipping  down  of  the  epithelium  cover- 
ing the  edge  of  the  jaw  into  the  underlying  connective  tissue  (mesoderm) 
where  it  forms  the  dental  shelf,  or  common  dental  germ.  Soon  after  the 
formation  of  the  dental  shelf,  a  groove  appears  along  the  margin  of  the 
jaw  where  the  ingrowth  of  epithelium  occurred.  This  is  known  as  the 
dental  groove.  The  epitheHum  of  the  dental  shelf  is  at  first  of  uniform 
thickness.  Soon,  however,  at  intervals  along  the  outer  side  of  the  den- 
tal shelf,  the  cells  of  the  shelf  undergo  proliferation  and  form  thicken- 
ings, ten  in  the  upper  and  ten  in  the  lower  jaw,  each  one  corresponding 
to  the  position  of  a  future  milk  tooth.  These  are  known  as  special 
dental  germs,  and  remain  for  some  time  connected  with  one  another  and 
with  the  surface  epithelium  by  means  of  the  rest  of  the  dental  ridge. 

Into  the  side  of  each  special  dental  germ  there  occurs  about  the  end 
of  the  third  month  (embryos  of  about  40  mm.)  an  invagination  of  the 
underlying  connective  tissue.  In  the  upper  jaw  the  invagination  takes 
place  on  the  upper  and  inner  side,  in  the  lower  jaw  on  the  lower  and 
inner  side,  of  each  dental  germ.  Each  invagination  forms  a  dental  papilla 
(Fig.  124),  over  which  the  tissue  of  the  special  dental  germ  forms  a  sort 
of  cap,  the  latter  being  known  from  its  subsequent  function  as  the 
enamel  organ,  the  papilla  itself  giving  rise  to  the  pulp  and  dentine.  The 
dental  germs  are  at  this  stage  connected  with  each  other  by  remaining 
portions  of  the  dental  shelf,  and  with  the  surface  epithelium  by  remains 


THE  DIGESTIVE  S^'STEM. 


207 


OMlSJSiLL '"»«: 


°o- 


Fig.  122. 


Fig.  12^. 


Fig.  124. 


Fig  .  1 2  s . 


Figs.  122,  123,  124,  125. — Four  Stages  in  the  Development  of  a  Tooth  (from  lower  jaw 
of  sheep  embryo).  (Bohm-DavidolT.)  Fig.  122,  Beginning  of  enamel  organ  showing  con- 
nection with  epithelium  of  mouth;  Fig.  123,  Later  stage  showing  same  with  iirst  trace 
of  papilla;  Fig.  124,  Later  stage  showing  papilla  well  formed,  the  ditlerentiation  of  the 
enamel  pulp  and  of  the  inner  and  outer  enamel  cells  can  be  seen;  odontoblast 
appearing  along  periphery  of  the  papilla;  Fig.  125  shows  also  beginning  enamel  organ  of 
permanent  tooth;  Figs.  122,  123,  124,  X  no,  Fig.  125,  X  40.  a,  Epithelium  of  mouth;  b, 
its  basal  layer;  c,  superficial  ceils  of  enamel  organ;  d,  enamel  pulp;  p,  dental  papilla;  s, 
enamel  cells;  c,  odontoblasts;  S,  enamel  organ  of  permanent  tooth  just  beginning  to 
differentiate;  v,  remains  of  enamel  ledge  of  milk  tooth;  u,  surrounding  ronnecti\c  tissue. 


208  THE  ORGANS. 

of  the  original  invagination.  The  next  step  is  the  almost  complete 
separation  of  the  special  dental  germs  and  ridge  from  the  surface  epithe- 
lium (Fig.  125),  and  the  formation  around  each  special  dei  tal  germ  of 
a  vascular  membrane,  the  dental  sac.  The  attenuated  strand  of  epithe- 
lial cells,  which  still  maintains  a  connection  between  the  dental  germs 
and  the  epithelium  of  the  gums,  is  known  as  the  neck  of  the  enamel  organ 
and  it  is  from  this  that  an  extension  soon  occurs  to  the  inner  side  of  the 


Fig.  126.— Developing  Tooth  from  Three-and-one-half-months'  Human  Embryo. 
X  65.  (Szymonowicz.)  a,  Epithelium  of  gums;  h,  neck  of  enamel  organ;  c,  dental  germ 
of  permanent  tooth;  d,  bone  of  lower  jaw;  e,  dental  papilla;/,  inner  enamel  cells;  g,^snamel 
pulp;  Ji,  outer  enamel  cells. 

dental  germs  of  the  milk  teeth,  to  form  the  dental  germs  of  the  perma- 
nent teeth  (Fig.  126,  c).  Into  the  latter,  connective-tissue  papillae  extend 
as  in  the  case  of  the  milk  teeth.  There  are  thus  present  as  early  as  the 
fifth  month  of  foetal  existence  the  germs  of  all  milk  and  of  some  perma- 
nent teeth. 

f'*^  The  ENAMEL  is  formed  by  the  enamel  organ.  At  the  stage 
represented  in  Fig.  128,  it  consists  of  three  layers:  (i)  The  outer  enamel 
cells,  somewhat  flattened;  (2)  the  inner  enamel  cells,  high  columnar 
epithelium;  (3)  a  layer  of  enamel   pulp,   situated   between  the    other 


THE  DIGESTIVE  SYSTEM. 


209 


layers,  and  consisting  of  stellate  anastomosing  cells  with  considerable 
intercellular  substance  (Figs.  128  and  129).  A  membrane,  the 
cuticular  membrane,  is  first  laid  down  between  the  inner  enamel  cells  and 
the  dentine.  Each  of  the  inner  enamel  cells  now  sends  out  a  process, 
Tomes''  process,  from  its  inner  end.  The  processes  are  separated  by  a 
considerable  amount  of  cement,  and  are  the  beginnings  of  the  enamel 
prisms.     Calcification  now  takes  place  both  in  the  prisms  and  in  the 


Epithelium  of  mouth 


enamel  cells 


Dental  sac 


Bone  of  jaw- 


Blood-vessel 


Papilla 

Fig.   127. — Longitudinal    section    of     a   developing    tooth    of    a    new-born    pupp_v 
(Bonnett).  late  stage. 

cement  substance,  beginning  in  the  ends  nearest  the  papilla.  As  this 
proceeds  outward,  the  prisms  become  much  elongated  and  the  cement 
substance  reduced  in  amount.  Further  growth  in  thickness  of  enamel 
occurs  by  lengthening  of  the  enamel  prisms.  During  the  formation  of 
the  enamel,  the  enamel  pulp  and  the  external  enamel  cells  disappear. 

The  formation  of  enamel  in  the  milk  teeth  begins  about  the  end  of 
the  fourth  month  and  continues  until  the  eruption  of  the  teeth.     The 
extent  of  the  enamel  organ  is  considerably  greater  than  that  of  the 
14 


210 


THE  ORGANS. 


enamel,  the  former  covering  the  entire  tooth,  both  root  and  crown, 
with  the  exception  of  the  base  of  the  papilla  where  the  latter  is  connected 
with  the  underlying  connective  tissue.  As  the  tooth  develops,  the 
enamel  organ  disappears  over  the  root,  remaining  to  form  the  enamel 
only  over  that  part  of  the  tooth  which  is  to  be  subsequently  exposed. 
The  function  of  the  enamel  pulp  is  not  known.  It  disappears  as  the 
tooth  growls.  It  has  been  suggested  that  it  may  furnish  nutrition  or 
serve  as  an  avenue  throush  which  nutrition  reaches  the  non-vascular 


Enamel 
Dentine  I  Enamel  prisms 


Outer 
Inner  J 


■  enamel  cells 


^-i —     Enamel  pulp 


Cuticle 


\  of  enamel  cells 


Basal  memb.  J 


Fig.  128. — Section  through  border  of  a  developing  tooth  of  a  new-born  puppy. 
(Bonnett). 

enamel  organ.     It  may  serve  as  an  area  of  least  resistance  through 
which  the  tooth  grows. 

The  DENTINE  is  the  first  of  the  dental  tissues  to  become  hard. 
Both  dentine  and  pulp  develop,  as  noted  on  p.  206,  from  the  meso- 
derm of  the  dental  papilla.  When  the  latter  is  first  formed  it  is  of  the 
same  structure  as  the  surrounding  mesoderm  with  which  it  is  contin- 
uous, except  that  it  is  somewhat  more  dense;  later  it  assumes  more  the 
character  of  embryonal  connective  tissue,  blood-vessels  and  nerves 
growing  into  it  from  the  underlying  connective  tissue.  The  most  periph- 
eral cells  of  the  pulp,  those  lying  nearest  the  enamel  organ,  differen- 
tiate from  the  rest  of  the  pulp  to  form  a  single  layer  of  columnar  or 


THE  DIGESTIVE  SYSTEM. 


211 


pyramidal  cells — the  odontoblasts.  The  outer  end  of  each  cell  is  broad, 
while  the  inner  end  which  contains  the  nucleus  narrows  to  a  point  from 
which  a  delicate  process  extends  into  the  pulp  and  probably  anasto- 
moses with  other  cell  processes.  These  cells  are  analogous  to  the  osteo- 
blasts of  developing  bone  and  Hke  them  appear  to  determine  the  de- 
position of  lime  salts.  The  lime 
salts  are  first  laid  down  in  a  mem- 
brane-like structure — the  membrana 
preformativa — which  the  odonto- 
blasts apparently  form  between 
themselves  and  the  enamel.  From 
this  membrane  the  transformation 
of  the  connective  tissue  into  dentine 
progresses  inward  toward  the  pulp, 
additional  dentine  continuing  to  be 
laid  down  in  layers, each  new  layer  in- 
ternal to  the  preceding.  In  this  way 
the  dental  papilla  is  reduced  in  size 
to  form  the  pulp  cavity.  In  the  outer 
part  of  the  dentine  spaces  remain  in 
which  no  lime  salts  are  deposited. 
These  are  the  interglobular  spaces. 
As  calcification  proceeds  the  odon- 
toblasts do  not  become  enclosed 
within  the  dentine  as  do  the  osteo- 
blasts within  bone.  They  leave 
merely  long  slender  processes,  the 
dental  fibres,  lying  in  minute  chan- 
nels through  the  dentine,  dental  canals,  while  the  bodies  of  the  cells 
form  a  single  layer  along  the  inner  margin  of  the  dentine.  There  are 
thus  no  lacunae  and  no  cells  within  the  dentine.  This  relation  of 
odontoblasts  to  dentine,  and  probably  the  original  odontoblasts,  per- 
sist, not  only  throughout  embryonic  but  through  adult  life. 

While  the  tooth  lies  within  the  gum,  the  somewhat  condensed  con- 
nective tissue  which  surrounds  it  constitutes  the  dental  sac. 

As  the  germs  of  the  milk  teeth  develop,  the  dental  shelf  broadens  by 
extending  inward  toward  the  tongue.  Along  this  inner  margin  appear 
the  germs  of  the  permanent  teeth,  the  de\-elopment  of  the  various 
teeth  structures  from  the  germs  Ijeing  identical  with  the  process  de- 
scribed in  the  case  of  the  milk  teeth. 


Fig.  129. — From  Cross-section  through  a 
Developing  Tooth.  X  720.  (Bohm  and 
von  Davidoff.)  Note  close  relationship 
between  odontoblasts  and  tissue  of  dental 
pulp,  a,  Dental  pulp;  b,  odontoblasts;  c, 
dentine;  d,  inner  enamel  cells;  e,  enamel 
pulp. 


212  '  THE  ORGANS. 

Twenty  of  the  permanent  teeth  correspond  in  position  to  the  twenty 
milk  teeth,  while  twelve  new  molar  germs,  six  in  the  upper  and  six  in 
the  lower  jaw,  represent  the  true  molars  of  the  adult.  The  first  perma- 
nent tooth  germ  to  appear  is  that  of  the  first  molar,  about  the  beginning 
of  the  fifth  month  (embryos  of  about  i8o  mm.).  It  lies  just  behind  the 
second  molar  of  the  milk  dentition.  The  germs  of  the  incisors  and 
canines  appear  about  the  end  of  the  sixth  month,  those  of  the  premolars, 
which  replace  the  milk  molars,  in  the  beginning  of  the  eighth  month. 
The  germs  of  the  second  and  third  (wisdom  teeth)  molars  do  not  ap- 
pear until  after  birth,  those  of  the  former  at  about  six  months,  of  the 
latter  during  the  fifth  year. 

The  CEMENTUM  is  developed  by  ossification  of  that  part  of  the  dental 
sac  which  covers  the  root,  its  development  being  similar  to  subperiosteal 
bone  formation  (p.  177),  without  the  formation  of  Haversian  systems. 

TECHNIC. 

(i)  Teeth  are  extremely  diificult  organs  from  which  to  obtain  satisfactory  ma- 
terial for  study.  Sections  of  hard  (undecalcified)  and  of  decalcified  teeth  may  be 
prepared  in  the  same  manner  as  sections  of  bone — technics  i,  p.  171;  2,  p.  172.  The 
decalcified  tooth  should  include  if  possible  the  alveolar  margin  of  the  jaw,  so  that 
in  longitudinal  sections  the  mode  of  implantation  and  the  relation  of  the  tooth  to 
the  surrounding  structures  can  be  seen. 

(2)  For  the  study  of  developing  teeth,  embryo  pigs,  sheep,  cats,  dogs,  etc.,  are 
suitable.  For  the  early  stages  foetal  pigs  should  be  five  to  six  inches  long;  for  the 
intermediate,  ten  to  twelve  inches.  The  later  stages  are  best  obtained  from  a  small 
new-born  animal,  e.g.,  kitten  or  small  pup.  The  jaw — preferably  the  lower — or 
pieces  of  the  jaw  are  fixed  in  formalin-Miiller's  fluid  (technic  5,  p.  7),  hardened 
in  alcohol,  and  decalcified  (page  9).  Subsequent  treatment  is  the  same  as  for  de- 
veloping bone  (technic  i,  p.  179). 

The  Pharynx. 

The  wall  of  the  pharynx  consists  of  three  coats — mucous,  muscular, 
and  fibrous. 

I.  The  mucous  membrane  has  a  surface  epithelium  and  an  un- 
derlying stroma. 

The  EPITHELIUM  is  stratified  squamous  except  in  the  region  of  the 
posterior  nares,  where  it  is  stratified  columnar  ciliated,  continuous 
with  the  similar  epithelium  of  the  nasal  mucosa. 

The  STROMA,  or  tunica  propria,  consists  of  mixed  fibrous  and 
elastic  tissue  infiltrated  with  lymphoid  cells.  In  certain  regions  these 
cells  form  distinct  lymph  nodules  (see  pharyngeal  tonsils,  page  157). 


THE  DIGESTR'E  SYSTEM.  213 

Beneath  the  stratified  squamous  epitheHum  the  stroma  is  thrown  up 
into  numerous  low  papillcp.  These  are  absent  in  regions  covered  by 
ciliated  cells.  Bounding  the  stroma  externally  is  a  strongly  developed 
layer  of  longitudinal  elastic  fibres,  the  elastic  limiting  layer,  which 
separates  the  stroma  from  the  muscular  coat  and  sends  stout  bands 
in  between  the  muscle  bundles  of  the  latter. 

2.  The  muscular  coat  lies  beneath  the  elastic  layer  and  is  formed 
of  very  irregularly  arranged  muscle  fibres  belonging  to  the  constrictor 
muscles  of  the  pharynx. 

3.  The  fibrous  coat  consists  of  a  dense  network  of  mixed  fibrous 
and  elastic  tissue.  It  has  no  distinct  external  limit,  and  binds  the 
pharynx  to  the  surrounding  structures. 

The  distribution  of  blood-vessels,  lymphatics,  and  nerves  is 
similar  to  that  in  the  oral  mucosa. 

Small,  branched,  tubular,  mucous  glands  are  present  in  the  stroma, 
and  extend  down  into  the  intermuscular  connective  tissue.  They 
are  most  numerous  near  the  opening  of  the  Eustachian  tube. 

TECHNIC. 

For  the  study  of  the  structure  of  the  walls  of  the  pharynx,  material  should 
be  prepared  as  in  technic  2,  p.  ig6. 

II.  THE  FOREGUT. 

The  (Esophagus. 

The  walls  of  the  oesophagus  are  continuous  with  those  of  the 
pharynx  and  closely  resemble  the  latter  in  structure.  They  consist 
of  four  layers,  which  from  within  outward  are  mucous,  submucous, 
muscular,  and  fibrous  (Fig.  130). 

1.  The  mucous  membrane  resembles  that  of  the  pharynx  except 
that  beneath  the  stroma  is  a  well-developed  muscularis  mucosce  com- 
posed of  smooth  muscle  cells  arranged  longitudinally.  The  muscularis 
mucosae  forms  a  complete  coat  only  in  the  lower  part  of  the  oesophagus. 
The  epithelium  is  stratified  squamous  and  rests  upon  a  papillated 
stroma. 

2.  The  submucosa  is  composed  of  loosely  arranged  fibrous  and 
elastic  tissue.  It  contains  mucous  glands,  the  larger  blood-vessels, 
lymphatics,  and  nerves. 

3.  The  Muscular  Coat. — In  tlic  upper  portion  of  the  oesophagus 
this  coat  is  composed  of  striated  muscle  fibres;  in  the  middle  portion. 


214 


THE  ORGANS. 


of  mixed  striated  and  smooth  muscle.  In  the  lower  portion  there  are 
two  distinct  layers  of  smooth  muscle,  an  inner  circular  and  an  outer 
longitudinal.     The  latter  is  not  continuous. 

4.  The  fibrous  coat  consists  of  bundles  of  white  fibrous  tissue  with 
many  elastic  fibres.  It  serves  to  connect  the  oesophagus  with  the 
surrounding  structures. 

Two  kinds  of  glands  occur  in  the  oesophagus. 


Fig.  130. — Transverse  Section  through  Wall  of  Dog's  CEsophagus.  X  18.  (Bohm 
and  von  Davidoff.)  a,  Epithelium;  b,  stroma;  c,  muscularis  mucosae;  d,  submucosa;  e, 
circular  muscle  layer;/,  longitudinal  muscle  layer;  g,  fibrous  layer. 

(i)  Mucous  Glands. — These  are  of  the  same  structure  as  those 
of  the  tongue,  but  much  smaller.  They  lie  in  the  submucosa  and  are 
distributed  throughout  the  entire  oesophagus,  though  most  numerous 
in  its  upper  third.  The  ducts  pass  obliquely  downward  on  their  way 
to  the  surface.  Just  before  entering  the  muscularis  mucosae  the  duct 
widens  out  to  form  a  sort  of  ampulla.  Beyond  this  it  again  becomes 
narrow  and  enters  the  epithelium  in  the  depression  between  two 
adjacent  papillae.  A  small  lymph  nodule  is  usually  attached  to  the 
duct  as  it  passes  through  the  tunica  propria. 

(2)  Simple  Branched  Tubular  Glands. — These  resemble  the 
glands  of  the  cardiac  end  of  the  stomach,  but  branch  much  more 


THE  DIGESTIVE  SYSTEM.  215 

profusely.  Some  contain  both  chief  and  acid  cells,  others  only  chief 
cells  (see  stomach,  page  219).  They  lie  in  the  tunica  propria,  and  are 
for  the  most  part  confined  to  a  narrow  zone  at  the  lower  end  of  the 
oesophagus  and  to  the  level  of  the  fifth  tracheal  ring.  Scattered  groups 
also  occur  in  other  regions. 

The  distribution  of  blood-vessels,  lymphatics,  and  ner\'es  in  the 
oesophagus  is  similar  to  their  distribution  in  the  mouth  (p.  195).  Be- 
tween the  two  muscular  coats  the  nerve  fibres  form  plexuses  in  which 
are  many  sympathetic  nerve  cells.  These  plexuses  are  analogous  to 
the  plexuses  of  Meissner  in  the  stomach  and  intestine. 

TECHNIC. 

Remove  a  portion  of  the  wall  of  the  oesophagus,  wash  carefully  in  normal 
salt  solution,  and  pin  out,  mucous-membrane  side  up,  on  a  piece  of  cork.  Fix  in 
formalin-Miiller's  fluid  and  harden  in  alcohol  (technic  5,  p.  7).  Transverse  or 
longitudinal  sections  should  be  cut  through  the  entire  thickness  of  the  wall.  If  the 
details  of  the  muscular  coat  are  to  be  studied,  sections  from  at  least  three  dif- 
ferent levels  should  be  taken:  one  near  the  upper  end,  one  at  about  the  middle,  and 
the  other  in  the  lower  third.  Stain  with  hasmatoxylin-eosin  or  haematoxylin-picro- 
acid-fuchsin  (technic  i,  p.  18;  3,  p.  19)  and  mount  in  balsam. 

General  Structure   of  the  Walls   of  the    Gastro-intestinal 

Canal. 

The  walls  of  the  stomach  and  intestines  are  made  up  of  four  coats 
(Fig.  131).  These  from  the  lumen  outward  are  mucous,  submucous, 
muscular,  and  serous. 

I.  The  mucous  membrane  (Fig.  131)  consists  of  surface  epithe- 
lium, glands,  stroma,  and  muscularis  mucosae.  The  surface  epithelium 
is  simple  columnar  and  rests  upon  a  distinct  basement  membrane.  The 
arrangement  of  the  glands  and  the  nature  of  the  gland  cells  differ  in 
different  parts  of  the  tract.  The  stroma  is  a  loosely  arranged,  richly 
cellular  connective  tissue,  which  in  many  places  is  so  infiltrated  with 
lymphoid  cells  as  to  constitute  dilTuse  lymphatic  tissue.  In  other  places 
it  contains  circumscribed  masses  of  lymphatic  tissue,  lymph  nodules. 
The  amount  of  stroma  depends  upon  the  closeness  with  which  the 
glands  are  packed.  The  muscularis  mucoscc  consists  of  smooth  muscle 
cells,  which  have  a  generally  longitudinal  arrangement.  Where, 
however,  the  muscularis  mucosae  is  thick  there  are  usually  two  distinct 
layers — an  inner  circular  and  an  outer  longitudinal.  Folds  of  con- 
siderable   extent    occur    in    the    mucous    membrane.     Those    of    the 


216 


THE  ORGANS. 


Stomach  are  known  as  rugcE,  and  are  not  constant,  depending  upon 
the  degree  of  distention  of  the  organ.  Those  of  the  small  intestine 
are  much  more  definite,  and  are  known  as  valvules  conniventes. 

2.  The  submucosa  (Fig.  131)  is  a  loose  connective-tissue  structure. 
It  contains  the  larger  blood-vessels,  lymphatics,  and  nerves. 


Fig.  131. — Diagram  of  Structure  of  Wall  of  Gastro-intestinal  Canal.  A,  Mucous 
membrane;  a,  glands;  b,  epithelium;  c,  goblet  cells;  d,  stroma;  e,  inner  circular;/,  outer 
longitudinal  layers  of  g,  muscularis  mucosae.  B,  Submucosa.  C,  Muscular  coat;  h,  its 
inner  circular  layer;  ],  its  outer  longitudinal  layer;  i,  intermuscular  connective-tissue 
septum.     D,  serous  coat;  k,  its  connective-tissue  layer;  /,  its  endothelial  layer. 

3.  The  muscular  coat  (Fig.  131)  consists  of  two  layers  of  smooth 
muscle,  which  in  the  intestine  are  sharply  differentiated  into  an  inner 
circular  and  an  outer  longitudinal.  In  the  stomach  the  direction  of  the 
layers  of  the  muscular  coat  is  less  definite.  A  narrow  layer  of  connect- 
ive tissue  separates  the  two  layers  of  muscle.  From  this,  septa  extend 
into  the  muscle  tissue,  separating  it  into  bundles. 


THE  DIGESTIVE  SYSTEM. 


217 


4.  The  serous  coat  (Fig.  131)  is  the  visceral  layer  of  the  peritoneum. 
It  consists  of  a  thin  layer  of  connective  tissue  covered  by  a  single  layer 
of  mesothelium.  Along  the  attachment  of  the  mesentery  the  serous 
coat  is  wanting. 

The  subdivisions  of  the  gastro-intestinal  canal  differ  from  one 
another  mainly  in  regard  to  the  structure  of  their  mucous  membranes, 
and  especially  in  regard  to  the  structure  of  the  glands  of  the  mucous 
membrane  and  submucosa. 


»■ 


cd 


Fig.  132. — Section  through  Junction  of  (Esophagus  and  Stomach  of  Man.      X  121 
(Schafer.)     Oe,  (Esophagus;  M,  stomach;  cd,  cardiac  glands;  u<d,  dilated  ducts  of  cardiac 
glands;  S,   stroma;  E,   stratified  squamous  epithelium  of  oesophagus;   mm,   muscularis 
mucosae;  cd,  irregularly  cut  tubules  of  cardiac  glands;  dd,  cardiac  glands  in  lower  end  of  the 
oesophagus;  il,  Hmit  of  stratified  oesophageal  epithelium. 


The  Stomach. 

At  the  junction  of  oesophagus  and  stomach  there  is  an  abrupt 
transition  from  the  stratified  squamous  epithelium  of  the  former  with 
its  smooth  surface  to  the  simple  columnar  cpithcHum  of  the  latter  with 
its  elevations  and  depressions.  In  the  deeper  structures  the  line  of 
demarcation  is  not  so  abrupt,  the  muscularis  mucosae  of  the  oesophagus 


218  THE  ORGANS. 

being  continuous  with  that  of  the  stomach,  and  glands  of  the  stomach 
type  extending  up  under  the  stratified  epithelium  of  the  oesophagus 
(Fig.  132). 

I.  The  mucous  membrane  of  the  stomach  is  folded  into  ridges  or 
nigce,  the  height  and  number  of  which  depend,  as  already  noted,  upon 
the  degree  of  distention  of  the  organ.  The  rugae  are  most  prominent 
in  the  collapsed  organ,  almost  absent  when  the  organ  is  fully  distended. 
In  addition  to  the  rugae  the  entire  mucous  membrane  is  studded  with 
minute  depressions  barely  A-isible  to  the  naked  eye,  the  so-called 
gastric  pits  (Fig.  134,  Mg).  These  mark  the  openings  of  the  gastric 
glands.     In   the   fundus   they   are   comparatively   shallow,   extending 


Gastric  pits 


Gastric  pits 


Fig.  133.^ — Surface  View  of  Mucous  Membrane  of  Stomach  showing  gastricfpits 
(Spalteholz). 

through  about  one-fifth  the  thickness  of  the  mucosa;  in  the  pylorus  the 
pits  are  much  deeper,  extending  through  half  or  more  of  the  thickness 
of  the  mucous  membrane  (compare  Figs.  134  and  137). 

The  Epithelium. — This  is  of  the  simple  columnar  type,  covers 
the  entire  surface  of  the  gastric  mucosa  and  extends  down  into 
the  pits  (Fig.  134).  The  cells  are  of  the  high,  clear,  mucous  type 
(Fig.  135,  M  and  M').  The  end  of  the  cell  toward  the  lumen  is  clear, 
usually  consists  mostly  of  mucous,  and  consequently  stains  lightly. 
There  is  no  such  distinct  cuticle  as  in  the  intestine.  The  basal  end  of 
the  cell  contains  the  spheroidal,  oval,  or  sometimes  flattened  nucleus,  is 
granular,  and  takes  a  darker  stain.  The  amount  of  mucus  in  the  cell 
depends  upon  its  functional  condition.  The  cells  rest  upon  a  distinct 
basement  membrane. 

The  Gastric  Glands. — Extending  from  the  bottoms  of  the  pits, 
their  epithelium  continuous  with  that  of  the  pits  themselves,  are  the 


THE  DIGESTIVE  SYSTET^I. 


219 


gastric  glands.  These  are  of  two  kinds,  peptic  or  fundus  glands,  dis- 
tributed throughout  the  greater  part  of  the  gastric  mucosa,  and  pyloric 
glands,  confined  to  the  immediate  region  of  the  pylorus. 

The  peptic  glands  (Fig.  134)  are 
simple,  sometimes  branched,  tubular 
glands,  of  which  from  three  to  seven 
open  into  each  gastric  pit.  They  ex- 
tend through  the  entire  thickness  of 
the  stroma,  to  the  muscularis  mucosae. 

Each  gland  consists  of  (i)  a  mouth 
opening  into  the  pit;  (2)  a  constricted 
portion,  the  neck;  (3)  the  body  or 
main  portion  of  the  tubule;  and  (4) 
a  slightly  dilated  and  bent  blind  ex- 
tremity, the  fundus  (Fig.  134).  The 
mouth  marks  the  transition  from  the 
higher  epithelium  of  the  pit  to  the  low 
cuboidal  of  the  neck  (Fig.  135,  /z).  In 
the  body  and  fundus  of  the  gland  two 
types  of  cells  are  found:  (a)  chief  cells 
(central,  peptic,  or  adelomorphous), 
and  [b)  parietal  cells  (acid,  oxyntic,  or 
delomorphous). 

The  chief  cells  (Fig.  135,  a)  are  the 
more  numerous.  They  are  of  the  low 
columnar  type,  often  pyramidal  with 
apices  directed  toward  the  lumen. 
Their  bases  rest  either  on  the  base- 
ment membrane  or  against  the  parietal 
cells.  The  appearance  which  these 
cells  present  depends  upon  their 
functional  condition  (p.  239).  They 
usually  appear  clear  and  granular  and 
take  a  light  stain. 

The  parietal  cells  (Fig.  135,  b) 
are  oval  or  polygonal  in  shape,  and 

lie  here  and  there  against  the  basement  membrane.  The  nucleus  is 
spherical,  somewhat  larger  than  that  of  the  chief  cell,  and  is  usually  situ- 
ated at  the  center  of  the  cell.  The  protoplasm  is  finely  granular  and  in 
the  fresh  unstained  condition  appears  clearer  than  that  of  the  chief 


Fig.  134. — Vertical  Section  through  the 
Mucous  Membrane  of  the  Fundus  of 
the  Stomach.  X85.  (Kolliker.)  Mg, 
Gastric  pits;  //,  neck;  k,  body;  g. 
fundus  of  peptic  glands;  h,  chief 
cells;  /),  parietal  cells;  m,  muscularis 
mucosa^. 


220 


THE  ORGANS. 


cells.  The  parietal  cells  stain  intensely  with  the  aniline  dyes  with  the 
result  that  in  stained  specimens  the  two  kinds  of  cells  are  in  marked 
contrast,  the  parietal  cells  being  much  darker  than  the  chief  cells. 
Although  lying  against  the  basement  membrane  and  frequently  push- 
ing it  out  so  as  to  form  little  protuberances  beyond  the  even  line  of  the 

gland  tubule,  the  parietal  cells 
always  maintain  a  connection  with 
the  lumen.  This  is  accomplished 
by  means  of  little  clefts  between  the 
chief  cells,  intercellular  secretory 
tubules,  which  extend  down  to  the 
parietal  cells.  By  means  of  the 
method  of  Golgi  may  be  demon- 
strated not  only  the  intercellular 
secretory  tubules,  but  also  the  fact 
that  upon  reaching  the  cells  these 
are  continuous  with  a  network  of 
minute  spaces  within  the  cell — the 
intracellular  secretory  tubules  (Fig. 
136).  Parietal  cells  are  not  dis- 
tributed uniformly  throughout  the 
gland,  but  are  most  numerous  in 
the  body,  where  they  frequently 
almost  obscure  the  chief  cells.  In 
the  fundus  of  the  gland  parietal 
cells  are  less  numerous.  For  this 
reason  and  because  of  the  wider  lumen  of  the  fundus,  transverse  and 
longitudinal  sections  of  this  part  of  the  tubule  are  most  satisfactory  for 
the  study  of  the  relations  of  the  two  kinds  of  cells  (Figs.  134  and  135). 
Lying  near  the  basement  membrane  among  the  bases  of  the  colum- 
nar epithelial  cells  are  small  spherical  or  irregular  cells  with  dark  nuclei. 
These  are  young  epithelial  cells  which  from  their  function  are  known 
as  "replacing  cells"  (see  page  65). 

The  PYLORIC  GLANDS  (Figs.  137  and  138)  are  simple  branched 
tubular  glands,  several  of  which  open  into  each  of  the  deep  pyloric  pits. 
The  glands,  though  short,  are  quite  tortuous,  so  that  in  sections  the 
tubules  are  seen  cut  mainly  transversely  or  obliciucly.  In  most  of  the 
pyloric  glands  but  one  type  of  cell  is  found.  These  resemble  the  chief 
cells  of  the  fundus,  but  yjrescnt  a  more  uniform  appearance,  probably 
due  to  the  absence  of  parietal  cells.     As  in  the  fundus,  "replacing  cells" 


Fig.  135. — Cross-sections  at  Various 
Levels  of  Peptic  Glands  of  Stomach. 
X  400.  (KoUiker.)  M,  Section  through 
gastric  pit  near  surface;  M',  section 
through  gastric  pit  near  bottom;  h, 
mouth  of  gland;  k,  neck;  g,  body  near 
fundus;  a,  chief  cells;  b,  parietal  cells. 


THE  DIGESTIVE  SYSTEM. 


221 


lie  between  the  bases  of  the  columnar  epithelial  cells.  Parietal  cells 
are  not  always  entirely  absent,  but  occur  here  and  there  in  the  pyloric 
tubules,  especially  near  the  fundus. 

The  transition  from  fundus  to  pylorus  is  not  abrupt,  but  is  marked 
by  a  "transitional  border  zone,"  in  which  fundus  and  pyloric  glands 
are  intermingled. 

In  the  transition  zone  between  oeso- 
phagus and  stomach  are  found  glands 
which  resemble  the  peptic  glands,  but  ^ 
contain  no  parietal  cells. 

The  STROMA  (Figs.  134  and  137)  or 
TUNICA  PROPRIA,  in  which  the  glands  are 
embedded,  consists  of  mixed  fibrillar  and 
reticular  connective  tissue  infiltrated  with 
lymphoid  cells.  In  the  fundus  of  the 
stomach  the  glands  are  so  closely  packed 
that  the  stroma  is  reduced  to  thin  strands, 
which  pass  up  between  the  glands  and 
also  separate  them  from  the  muscularis 
mucosae.  In  the  pylorus  the  glands  are 
more  widely  separated  and  the  stroma 
is  correspondingly  greater  in  amount. 
In  both  fundus  and  pylorus  thicker 
strands  of  stroma  surround  a  number  of 
gland  tubules,  thus  separating  them  into 

more  or  less  well-defined  groups.  In  addition  to  the  diffuse  lym- 
phatic tissue  of  the  stroma,  closely  packed  aggregations  of  lymphoid 
cells  are  found  in  the  shape  of  distinct  nodules,  known  as  ''solitary 
follicles.''  These  occur  throughout  the  entire  gastric  mucosa,  but  are 
most  numerous  in  the  pylorus.  The  nodules  are  usually  egg-shaped, 
their  apices  lying  just  beneath  the  epithehum,  their  bases  resting  upon 
the  muscularis  mucosae.  Less  commonly  they  lie  partly  in  the  sub- 
mucosa.  Over  the  nodules  the  epithelium  is  more  or  less  infiltrated 
with  migratory  leucocytes.  Most  of  the  nodules  contain  germinal 
centres,  around  which  the  lymphoid  cells  are  more  closely  packed 
than  elsewhere  (see  page  148). 

The  MUSCULARIS  Mucos.E  (Figs.  134  and  137,  ;;/)  may  con- 
sist of  a  single  layer  of  smooth  muscle  with  cells  arranged  longi- 
tudinally or  obliquely,  or  there  may  be  two  distinct  layers,  an  iinier 
circular   and    an   outer   longitudinal.      From    the   muscularis   mucosas 


Fig.  136. — Longitudinal  Section  of 
Fundus  of  Gland  from  Pyloric 
End  of  Dog's  Stomach.  (Golgi 
method.  See4,  p.  26.)  a,  Lumen 
of  gland;  h,  intracellular  canals  in 
parietal  cells;  c,  cut-off  portion  of 
parietal  cell;  d,  chief  cells;  e, 
intercellular  canals  leading  from 
lumen  of  gland  to  canals  in 
parietal  cells. 


999 


THE  ORGANS. 


single  cells  and  groups  of  cells  extend  into  the  stroma  between  the 
gland  tubules. 

2.  The  submucosa  consists  of  connective  tissue,  loosely  arranged, 
many  elastic  fibres,  and  some  fat.  It  contains  the  larger  blood-vessels 
and  nerves,  including  the  plexus  of  Meissner  (p.  238). 


ililill 


Fig.  137.  Fig.  138. 

Fig.  137. — Vertical  Section  through  Mucous  Membrane  of  Pyloric  End  of  Stomach. 
X  85.  (KoUiker.)  Mg,  Gastric  pit;  b,  blood-vessel  in  stroma;  d,  longitudinal  section 
of^body  of  gland;  m,  muscularis  mucosse. 

Fig.  138. — Pyloric  Gland  from  Vertical  Section  through  Wall  of  Dog's  Stomach. 
(Ebstein.)  m,  Gastric  pit  in  which  are  seen  some  transversely  cut  cells;  n,  neck  of  gland; 
/,  fundus  cut  transversely. 

3.  The  muscular  coat  is  usually  described  as  consisting  of  three 
layers,  an  inner  oblique,  a  middle  circular,  and  an  outer  longitudinal. 

In  the  fundus  the  muscle  bundles  run  in  various  directions  so  that 
the  division  of  the  muscular  coat  into  layers  having  definite  directions 
can  be  made  out  only  in  the  ]>ylorus.  Here  the  inner  and  middle 
layers  are  thickened  to  form  the  sphincter  pylori.  In  the  connective 
tissue  which  separates  the  groups  of  muscle  cells  are  collections  of 


THE  DIGESTIVE  SYSTEM.  223 

sympathetic  nerve  cells  and  fibres  which  while  much  less  distinct  are 
analogous  to  Auerbach's  plexus  of  the  intestine. 

4.  The  serous  coat  consists  of  a  layer  of  loosely  arranged  con- 
nective tissue  covered  by  a  single  layer  of  mesothelium. 

TECHNIC. 

(i)  Remove  a  human  stomach  (not  more  than  two  or  three  hours  after  death) 
or  that  of  a  recently  killed  dog.  Open  along  the  lesser  curvature,  and  carefully  re- 
move the  excess  of  mucus  by  washing  with  normal  saline.  Cut  pieces  through 
the  entire  thickness  of  the  wall,  one  from  the  fundus  and  one  from  the  pylorus; 
pin  out,  mucus  membrane  side  up,  on  pieces  of  cork,  fix  in  formalin-Miiller's  fluid 
(technic  5,  p.  7)  or  in  Zenker's  fluid  (technic  9,  p.  8),  and  harden  in  alcohol.  Sec- 
tions are  cut  as  thin  as  possible,  care  being  taken  that  the  plane  is  such  that  the 
glands  are  cut  longitudinally,  stained  with  haematoxylin-eosin  (technic  i,  p.  18), 
and  mounted  in  balsam. 

(2)  Instead  of  removing  pieces  of  stomach  and  pinning  them  out  on  cork,  as 
suggested  in  the  preceding  technic,  the  entire  stoma(^  may  be  filled  with  the  fixa- 
tive, the  ends  being  tied,  and  then  placed  in  a  large  quantity  of  the  fixing  fluid. 
After  fixation,  pieces  are  removed  and  hardened  in  graded  alcohols.  If  this 
method  is  used,  great  care  must  be  taken  not  to  overdistend  the  organ,  only  very 
moderate  distention  being  desirable.  Further  treatment  is  the  same  as  in  the  pre- 
ceding technic  (i). 

(3)  For  comparison  of  resting  with  active  gastric  cells,  preparations  should  be 
made  from  the  stomach  of  an  animal  that  has  been  for  from  twenty-four  to  forty- 
eight  hours  without  food,  and  from  a  stomach  during  active  digestion.  Fix  in 
Zenker's  fluid  as  in  technic  (i),  above.  Examine  unstained  sections  and  sections 
stained  with  haematoxylin-eosin. 

(4)  Sections  through  the  junction  of  oesophagus  and  stomach  and  through  the 
junction  of  stomach  and  duodenum  furnish  instructive  pictures.  They  should  be 
prepared  as  in  technic  (i). 

(5)  For  the  study  of  the  distribution  of  the  blood-vessels  sections  of  an  injected 
stomach  should  be  made.  This  is  best  accompUshed  by  selecting  a  small  animal, 
such  as  a  rat  or  guinea-pig,  and  injecting  in  tola  through  the  ascending  aorta,  or 
by  injecting  only  the  hind  part  of  the  animal  through  the  abdominal  aorta.  Tech- 
nic, p.  22. 

III.  THE  MIDGUT. 

The  Small  Intestine. 

On  passing  from  stomach  to  small  intestine  the  rugcT  of  the  former 
disappear,  but  are  replaced  by  much  more  definite  foldings  of  the 
mucosa,  the  valvidcc  coiuiivcntcs  (Fig.  140).  These  folds  involve  the 
entire  thickness  of  the  mucous  membrane  and  part  of  the  submucosa. 
They  are  in  general  parallel  to  one  another,  and  pass  in  a  circular  or 


224 


THE  ORGANS. 


oblique  manner,  partly  around  the  lumen  of  the  gut.  The  entire 
surface  of  the  intestine,  including  the  valvulae,  is  studded  with  minute 
projections  just  visible  to  the  naked  eye,  and  known  as  villi  (Figs.  141 
and  142).  These  involve  only  the  epithelium  and  stroma,  although 
they  also  contain  some  muscular  elements  derived  from  the  muscularis 
mucosae.  The  villi  differ  in  shape  in  the  different  parts  of  the  small 
intestine,  being  leaf-shaped  in  the  duodenum,  rounded  in  the  jejunum, 
club-shaped  in  the  ileum.  The  valvules  conniventes  and  the  villi  are 
characteristic  of  the  small  intestine.     It  is  important  to  note  that 


Fig.  139. — Section  through  Junction  of  Pylorus  and  Duodenum.  (Klein.)  v,  Villi  of 
duodenum;  d,  stomach,  showing  gastric  pits;  b,  apex  of  a  solitary  lymph  nodule;  c,  crypt 
of  Lieberklihn;  s,  secreting  tubules  of  Brunner's  glands;  g,  pyloric  glands;  t,  tubules  of 
B runner's  glands  in  submucosa  of  stomach;  m,  muscularis  mucosa. 

while  the  pits  of  the  stomach  are  depressions  in  the  mucous  membrane, 
the  intestinal  villi  are  definite  projections  above  its  general  surface 
(Fig.  139). 

The  wall  of  the  intestine  consists  of  the  same  four  coats  described 
as  constituting  the  wall  of  the  stomach,  mucosa,  submucosa,  muscularis, 
and  serosa. 

i.  The  mucosa,  as  in  the  stomach,  is  composed  of  a  lining  epithe- 
lium, stroma,  f^lands,  and  muscularis  mucosa'.  Of  these  the  epithelium, 
the  stroma,  and  cells  from  the  muscularis  mucosae  are  concerned  in 
the  formation  of  the  villi. 

The  VILLUS  consists  of  a  central  core — a  fold  of  the  stroma — of 


THE   DIGESTIVE   SYSTEM. 


225 


mixed  fibrous  and  reticular  tissue  infiltrated  with  lymphoid  cells,  and 
of  a  covering  epithelium. 

The  epithelium  is  of  the  simple  columnar  type.  The  cells  are 
high  and  have  thickened  striated  free  borders  (Figs.  143  and  144). 
These  contiguous  thickened  free  borders  unite  to  form  a  distinct 
membrane,  the  cuticular  membrane  (Fig.  144,  c).  Scattered  among 
the  columnar  cells  are  numerous  mucous  or  goblet  cells  (Figs.  143  and 
144,  b).     The  goblet  cells  are  derived  from  the  columnar  cells,  and 


Fig.  140.— Vertical  Longitudinal  Section  of  Human  Jejunum  (X  i6)  (Stohr),  includ- 
ing two  valvulas  conniventes.  a,  Villi,  in  many  of  which  the  stroma  has  shrunken  away 
from  the  epithelium  leaving  a  clear  space,  X  X .  Lying  free  in  the  lumen  of  the  gut  are 
seen  sections  of  villi  cut  in  various  directions,  b.  Epithelium;  c,  stroma;  d,  crj-pts  of 
Lieberktihn;  X,  solitary  lymph  nodule  with  germinal  centre;  e,  tissue  of  subriiucosa 
forming  centre  of  one  of  the  valvule  conniventes;/,  submucosa;  g,  inner  circular  layer 
of  muscle;  //,  outer  longitudinal  layer  of  muscle;  /,  Auerbach's  ple.xus;  j,  serous  coat. 

vary  in  appearance  according  to  the  amount  of  secretion  which  thev 
contain.  A  cell  at  the  beginning  of  secretion  contains  onlv  a  small 
amount  of  mucus  near  its  free  border.  As  secretion  increases  the 
mucus  gradually  replaces  the  cytoplasm  until  the  latter  is  represented 
only  by  a  crescentic  mass  containing  a  flattened  nucleus  and  pressed 
against  the  basement  membrane.  The  cell  now  discharges  its  mucus 
upon  the  free  surface.  The  goblet  cells  possess  no  thickened  border, 
appearing,  when  seen  from  the  surface,  as  openings  surrounded  on  all 


226 


THE  ORGANS. 


sides  by  the  cuticulse  of  the  adjacent  columnar  cells.  Small  spherical 
cells  with  deeply  staining  nuclei  are  found  in  varying  numbers  among 
the  epithelial  cells.     These  are  so-called  wandering  cells,   migratory 


Mouths  of  crypts. 


Lymph  nodules 


Villi. 


Fig.   141. — Surface  View  of  Small  Intestine  near  upper  end,  showing 
villi  and  one  solitary  lymph  nodule.  X   12.   (Spalteholz). 


/    - 


.j-m^'---"'' 


Fig.  142. — Vertical  Section  through  Mucous  Membrane  of  Human  Jejunum.  X  80. 
(Stohr.)  a  and  b,  Artifacts  due  to  shrinkage;  c,  intestinal  crypts  (Lieberklihn);  d,  oblique 
and  transverse  sections  of  crypts;  e,  stroma;/,  e])ithe]ium;  ,^,  tangenlialiy  cut  villi;  h, 
muscuiaris  mucosa;;  i,  submucosa. 


THE  DICiESTR'E  SYSTEM. 


227 


leucocytes,  from  the  underlying  stroma  (Figs.  143,  /z,  and  144,  /). 
Other  cells  with  dark-staining  nuclei,  ''replacing  cells,''  are  found  be- 
tween the  bases  of  the  columnar  cells  (pages  65  and  220J. 

In  addition  to  the  connective-tissue  and  lymphoid  cells,  which 
constitute  the  main  bulk  of  the  villus  core  (Figs.  143  and  144),  isolated 
smooth  muscle  cells  derived  from  the  muscularis  mucosae  occur,  run- 


Fig.  143.  Fig.  144. 

Fig.  143. — Longitudinal  Section  of  Villus  from  Small  Intestine  of  Dog.  (Piersol.) 
a,  Columnar  epithelium;  b,  goblet  cells;  h,  leucocytes;  c,  basement  membrane;  d,  core  of 
villus;  e,  blood-vessels;  /,  lacteal. 

Fig.  144. — Cross-section  of  a  Villus  of  Human  Small  Intestine.  X  530.  (Kolliker.) 
The  stroma  of  the  villus  has  shrunken  away  from  the  epithelium,  b,  Goblet  cell;  c,  cuticula 
showing  striations;  e,  columnar  epithelial  cell;  gm,  basement  membrane  with  nuclei;  /, 
leucocyte  in  epithelium;  /',  leucocyte  just  beneath  epithelium;  «2,  large  leucocyte  in  stroma; 
ch,  central  chyle  vessel;  g,  blood-vessel. 

ning  in  the  long  axis  of  the  villus.  A  single  lymph  or  chyle  vessel  (Fig. 
143,  /,•  144,  ch)  with  distinct  endothelial  walls  traverses  the  centre  of 
each  villus,  ending  at  its  tip  in  a  slightly  dilated  blind  extremity.  As  it 
is  usually  seen  collapsed,  it  appears  as  two  closely  approximated  rows 
of  flat  cells  with  bulging  nuclei.  The  capillaries  of  the  villus  lie  for 
the  most  part  away  from  the  chyle  \-essel,  just  beneath  the  basement 
membrane  (Fig.  143,  e;  144,  "'). 

From  the  depths  of  the  depressions  between  the  villi.  sim])k'  tulnilar 


228 


THE  ORGANS. 


:l 

Q 

'■^ . 

glands — glands  or  crypts  of  Lieberkiihn  (Figs.  142  and  145) — extend 
down  through  the  stroma  as  far  as  the  muscularis  mucosas.  These 
crypts  are  lined  with  an  epithelium  similar  to  and  continuous  with  that 
covering  the  \i\\\.  The  cells  are,  however,  lower,  and  there  are  fewer 
goblet  cells.  In  addition  to  these  cells  there  are  also  found  in  the  depths 
of  the  crypts  of  Lieberkiihn  peculiar  coarsely  granular  cells,  the  cells 

of  Paneth  (Fig.  145,  k).  They  are  found 
in  man  and  in  rodents,  but  do  not  occur 
in  the  carnivora.  They  probably  pro- 
duce a  specific  secretion,  the  nature  of 
which  is  unknown. 

The  stroma,  besides  forming  the  cen- 
tres of  the  villi,  fills  in  the  spaces  between 
the  crypts  of  Lieberkiihn  and  between 
the  latter  and  the  muscularis  mucosas. 
In  places  the  lymphoid  cells  are  closely 
packed  to  form  distinct  nodules  or 
"solitary  follicles,"  such  as  are  found  in 
the  stomach  (see  page  221). 

Peyer's  Patches  (agminated  folh- 
cles)  (Fig.  146). — These  are  groups  of 
lymph  nodules  found  mainly  in  the  ileum, 
especially  near  its  junction  with  the  jeju- 
num. They  always  occur  on  the  side  of 
the  gut  opposite  to  the  attachment  of  the 
mesentery.  Each  patch  consists  of  from 
ten  to  seventy  nodules,  so  arranged  that 
the  entire  patch  has  a  generally  oval 
shape,  its  long  diameter  lying  lengthwise 
of  the  intestine.  The  nodules  of  which 
a  patch  is  composed  lie  side  by  side.  Their  apices  are  directed 
toward  the  lumen  and  project  almost  through  the  mucosa,  being 
uncovered  by  villi,  a  single  layer  of  columnar  epithelium  alone 
separating  their  surfaces  from  the  lumen  of  the  gut.  The  bases  of 
the  nodules  arc  not  confined  to  the  stroma,  but  usually  spread  out  in 
the  submucosa.  The  relation  of  the  patch  to  the  stroma  and  sub- 
mucosa  can  be  best  appreciated  by  following  the  course  of  the  mus- 
cularis mucos£e.  This  is  seen  to  stop  abruptly  at  the  circumference  of 
the  patch,  appearing  throughout  the  patch  as  isolated  groups  of  smooth 
muscle  cells.     The  nodules  rarely  remain  distinct,  but  are  confluent 


Fig.  145. — Longitudinal  Section  of 
Fundus  of  Crypt  of  Lieberkiihn. 
X530.  (Kollilier.)  5,  Goblet  cell 
showing  mitosis;  e,  epithelial  cell; 
k,  cell  of  Paneth;  /,  leucocyte  in 
epithelium;  m,  mitosis  in  epithelial 
cell.  Surrounding  the  crypt  is 
seen  the  stroma  of  the  mucous 
membrane. 


THE  DIGESTR'E  SYSTEM. 


229 


Fig.  146. — Transverse  Section  of  Cat's  Small  Intestine  through  a  Peyer's  Patch. 
(Stohr.)  a,  Villi;  b,  crypts;  c,  longitudinal  muscle  layer;  d,  circular  muscle  layer;  e,  lymph 
nodules;/,  muscularis  mucoste;  g,  submucosa. 


Solitary 
lymph  nodules 


Peyer's  patch 


Fig.  147. — Surface  View  of  Mucous  Membrane  of  Small  Intestine  (Ileum"),  showing 
Peyer's  patch  (Spalteholz). 


?:30 


THE  ORGANS. 


with  the  exception  of  their  apices  and  bases.  It  should  be  noted  that 
both  sohtary  nodules  and  Peyer's  patches  are  structures  of  the  mucosa, 
and  that  their  presence  in  the  submucosa  is  secondary. 

The  muscularis  mucosae  (Figs.  142  and  148)  consists  of  an  inner 
circular  and  an  outer  longitudinal  layer  of  smooth  muscle. 

2.  The  submucosa  (Figs. 
140,  142,  148)  consists,  as  in  the 
stomach,  of  loosely  arranged 
connective  tissue  and  contains 
the  larger  blood-vessels.  It  is 
free  from  glands  except  in  the 
duodenum,  where  it  contains 
the  glands  of  Brunner  (Fig. 
148).  These  are  branched 
tubular  glands  lined  with  a 
granular  columnar  epithelium 
similar  to  that  of  the  pyloric 
glands.  The  ducts  are  also 
lined  with  simple  columnar 
epithelium.  They  pass  through 
the  muscularis  mucosae  and 
empty  either  into  a  crypt  of 
Lieberkiihn  or  on  the  surface 
between  the  villi.  Brunner's 
glands  frequently  occur  in  the 
pylorus,  and  it  is  not  uncom- 
mon for  the  pyloric  glands  to 
extend  downward  somewhat 
into  the  duodenum.  Meissner^s 
plexus  of  nerve  fibres,  mingled  with  groups  of  sympathetic  ganglion 
cells,  lies  in  the  submucosa  (see  page  238). 

3.  The  muscular  coat  (Figs.  140  and  148)  consists  of  two  well- 
defined  layers  of  smooth  muscle,  an  inner  circular  and  an  outer  longi- 
tudinal. Connective-tissue  septa  divide  the  muscle  cells  into  groups 
or  bundles,  while  between  the  two  layers  of  muscle  is  a  connective- 
tissue  septum  which  varies  greatly  in  thickness  at  different  places  and 
contains  a  plexus  of  nerve  fibres  and  sympathetic  ganglion  cells  known 
as  the  plexus  of  Auerbach  (see  page  238). 

4.  The  serous  coat  consists  as  in  the  stomach  of  loose  connective 
tissue  covered  by  a  single  layer  of  mesothelium. 


'  •■•■••'■-••■•"••■-.^••j;_ 

Fig.  148. — From  Vertical  Longitudinal  Section 
of  Cat's  Duodenum  to  show  Brunner's 
Glands.  (Larrabee.)  a,  Villus;  h,  epithe- 
lium; c,  stroma;  d,  glands;  e,  muscularis 
mucosae;  /,  Brunner's  glands;  ,§•,  submucosa; 
h,  circular  muscle  layer. 


THE  DIGESTR'E  SYSTEM. 


231 


IV.  THE  ENDGUT. 

The  Large  Intestine. 

The  wall  of  the  large  intestine  consists  of  the  same  four  coats 
which  have  been  described  as  constituting  the  walls  of  the  stomach 
and  small  intestine,  mucous,  submucous,  muscular,  and  serous. 


Fig.  149.  Fig.  150. 

Fig.  i4g. — From  Vertical  Longitudinal  Section  of  Cat's  Large  Intestine.  (Larrabee.) 
a,  Epithelium;  h,  stroma;  c,  fundus  of  gland;  d,  muscuiaris  mucosa^;  e,  submucosa;/,  cir- 
cular muscle  layer;  g,  longitudinal  muscle  layer;  h,  serous  coat;  /,  Auerbach's  plexus. 

Fig.  150. — From  Vertical  Longitudinal  Section  of  the  IMucous  Membrane  of  the 
Human  Large  Litestine.  (Technic  i,  p.  241.)  a,  Mucous  (goblet)  cells;  h.  fundus  of  a 
gland  cut  obli(|uely;  c,  muscuiaris  mucosa;;  d,  lumen  of  a  gland  cut  longitudinally;  e,  stroma 
between  the  glands;/,  leucocytes  in  the  epithelium;  g,  stroma  between  fundi  of  glands  and 
muscuiaris  mucosa;. 


I.  The  mucous  membrane  has  a  comparatively  smooth  surface, 
there  being  neither  pits  as  in  the  stomach  nor  villi  as  in  the  small 
intestine  (Fig.   149).     The  glands  are  of  the  simple  tubular  variety, 


232  THE  ORGANS. 

are  considerably  longer  than  those  of  the  small  intestine,  are  almost 
straight,  and  extend  through  the  entire  thickness  of  the  stroma. 
Owdng  to  the  closeness  with  which  the  gland  tubules  are  packed,  the 
amount  of  stroma  is  usually  small.  The  surface  cells  (Fig.  149,  a) 
are  very  high  and  narrow,  with  small,  deeply  placed  nuclei,  and  are 
not  usually  intermingled  with  goblet  cells.  Passing  from  the  surface 
down  into  the  glands,  the  cells  become  somewhat  lower  and  goblet 
cells  become  numerous  (Fig.  150,  a  and  d).  Both  superficial  and 
deep  cells  rest  upon  a  basement  membrane  similar  to  that  in  the  small 
intestine.  The  stroma  also,  though  less  in  amount,  is  similar  in  struc- 
ture  to  the  stroma  of  the  small  intestine. 

The  MuscuLARis  MUCOS.5:  (Fig.  150,  c)  consists  of  an  inner  circular 
and  an  outer  longitudinal  layer  of  smooth  muscle. 

2.  The  submucosa  (Fig.  149,  e)  consists  of  loosely  arranged  con- 
nective tissue.  It  contains  large  blood-vessels  and  the  nerve  plexus 
of  Meissner  (see  page  238).  Solitary  lymph  follicles  occur  throughout 
the  mucous  membrane  of  the  large  intestine.  While  properly  con- 
sidered as  structures  of  the  stroma  from  which  they  originate,  the 
follicles  lie  mainly  in  the  submucosa.  (For  details  of  structure  see 
page  148.) 

3.  Of  the  muscularis  (Fig.  149)  the  inner  circular  layer  only  is 
complete,  the  muscle  tissue  of  the  external  longitudinal  coat  being 
arranged  mainly  as  three  strong,  flat,  longitudinal  bands,  the  lineae  coli. 
Between  these  bands  the  longitudinal  muscular  coat  is  either  very  thin 
or  entirely  absent.  In  the  connective  tissue,  lying  to  the  outer  side 
of  the  circular  muscle  coat,  is  the  nerve  plexus  of  Auerbach.  (For 
details  see  page  238.) 

4.  The  serous  coat  consists,  as  in  the  stomach  and  small  intestine, 
of  loose  connecti\'e  tissue  covered  by  a  single  layer  of  mesothelium. 

The  Vermiform  Appendix. 

The  vermiform  appendix  is  a  diverticulum  from  the  large  intestine. 
Its  walls  arc  continuous  with  those  of  the  latter,  and  closely  resemble 
them  in  general  structure.  There  are  the  same  four  coats,  mucous, 
submucous,  muscular,  and  serous. 

T.  The  mucous  membrane  (Fig.  151)  consists  of  epithelium, 
glands,  stroma,  and  muscularis  mucosae.  The  epithelium  resembles 
that  of  the  large  intestine.  The  glands  vary  in  number,  but  are  usually 
much  less  closely  packed  than  in  the  large  intestine.     They  are  most 


THE  DIGESTWE  SYSTEM. 


233 


numerous  in  the  appendices  of  infants  and  children.  The  gland 
tubules  (Fig.  151,  /')  are  usually  rudimentary,  but  in  most  cases  have  the 
same  structure  as  the  intestinal  glands,  and  are  evidently  functional 
as  they  contain  mucous  cells  in  all  stages  of  secretion.  In  consequence 
of  the  wider  separation  of  the  tubules  the  stroma  is  more  abundant  than 
in  the  large  intestine,  but  has  the  same  structure.     The  muscularis 


K^  ^   ^ 


^%\ 


i 


^v 


Fig.  151. — Transverse  Section  of  Human  \'ermiform  Appendi.x.  (Teclinic  2,  p.  241.) 
a,  Mesoappendix;  h,  serous  membrane  (serosa);  f,  outer  longitudinal  muscle  layer;  d,  inner 
circular  muscle  layer;  e,  submucosa;/,  groups  of  fat  cells  in  submucosa;  g,  blood-vessels 
in  submucosa;  h,  lymph  nodules;  /,  stroma;  ],  glands  opening  into  lumen  and  cut  in  various 
planes;  muscularis  mucosae  not  present. 

mucosa  is  usually  fairly  distinct  as  a  thin  circularly  disposed  band 
of  smooth  muscle  cells  just  beneath  the  stroma.  It  is  not  always 
present.  In  some  cases  the  mucosa  as  such  is  practically  absent, 
being  replaced  by  fibrous  tissue.  This  condition  is  especially  common 
after  middle  age,  and  may  or  may  not  be  associated  with  obliteration  of 
the  lumen. 

2.  The  submucosa  (Fig.  151,  e)  is  similar  to  that  of  the  intestine. 


234  THE  ORGANS. 

3.  The  muscular  coat  varies  greatly,  both  as  to  thickness  and 
as  to  the  amount  of  admixture  of  fibrous  tissue.  The  inner  circular 
layer  (Fig.  151,  d)  is  usually  thick  and  well  developed.  The  outer 
longitudinal  layer  (Fig.  151,  c)  differs  from  that  of  the  large  intestine 
in  having  no  arrangement  into  lineas,  the  muscle  tissue  forming  a  con- 
tinuous layer.  Less  commonly  a  more  or  less  marked  tendency  to  an 
arrangement  of  the  cells  of  the  longitudinal  coat  into  bundles,  between 
which  the  outer  coat  is  thin  or  wanting,  is  observed. 

4.  The  serosa  has  the  usual  structure  of  peritoneum. 

The  lymph  nodules  (Fig.  151,  h)  constitute  the  most  conspicuous 
feature  of  the  appendix.  They  lie  mainly  in  the  submucosa.  In 
children  and  young  adults  the  nodules  are  oval  or  spherical;  in  later 
life  somewhat  flattened.  The  nodules  may  be  entirely  distinct,  or 
may  be  arranged  as  in  a  Peyer's  patch  with  distinct  apices  and  bases, 
but  with  their  central  portions  confluent.  The  muscularis  mucosae 
either  passes  through  the  superficial  portions  of  the  nodules,  or,  where 
they  are  separated  from  the  lumen,  passes  over  them. 

The  distribution  of  blood-vessels,  lymphatics,  and  nerves  is 
similar  to  that  in  the  large  intestine. 

The  Rectiun. 

1.  The  mucous  membrane  of  the  rectum  has  a  structure  similar 
to  that  of  the  large  intestine.  The  glands  are  longer  and  the  mucosa 
is  consequently  somewhat  thicker.  In  the  lower  part  of  the  rectum 
definite  longitudinal  foldings  of  the  mucosa  occur,  the  so-called  col- 
umnce  rectales.  A  change  in  the  character  of  the  mucous  membrane 
begins  at  the  upper  end  of  the  columnse  rectales.  Here  the  simple 
columnar  epithelium  of  the  gut  passes  over  into  a  stratified  squamous 
epithelium,  beneath  which  is  a  papillated  stroma.  The  glands  con- 
tinue for  a  short  distance  beyond  the  change  in  the  epithelium,  but  soon 
completely  disappear.  At  the  anus  there  is  a  transition  from  mucous 
membrane  to  skin  similar  to  that  described  as  occurring  at  the  margin 
of  the  lips  (page  193). 

2.  The  submucosa  is  similar  in  structure  to  that  of  the  large 
intestine. 

The  muscularis  of  the  rectum  differs  from  that  of  the  large  in- 
testine in  that  the  longitudinal  layer  is  continuous  and  thick. 

The  serous  coat  is  absent  in  the  lower  part  of  the  rectum,  being 
replaced  l;y  a  fibrous  connective-tissue  layer,  which  connects  the  rec- 
tum with  the  surrounding  structures. 


THE  DIGESTIVE  SYSTEM.  235 

The  Peritoneum,  Mesentery,  and  Omentum. 

The  peritoneum  (see  also  p.  144)  is  a  serous  membrane  which  Hnes 
the  walls  of  the  abdomen  (parietal  peritoneum)  and  is  reflected  over 
the  contained  viscera  (visceral  peritoneum).  It  consists  of  two  layers, 
a  connective-tissue  stroma  and  mesothelium.  The  stroma  consists 
of  loosely  arranged  connective-tissue  bundles,  which  interlace  in  a 
plane  parallel  to  the  surface.  There  are  numerous  elastic  fibres,  espe- 
cially in  the  deeper  layer  of  the  parietal  peritoneum.  There  are 
comparatively  few  connective-tissue  cells.  The  mesothelium  consists 
of  a  single  layer  of  flat  polygonal  cells  with  bulging  nuclei.  The  cells 
have  irregular  wavy  outlines,  which  are  easily  demonstrated  with  silver 
nitrate  (Fig.  26).  The  shape  of  the  cells  varies  considerably  accord- 
ing to  the  direction  in  which  the  tissues  are  stretched.  Over  some  parts, 
e.g.,  the  liver  and  intestine,  the  peritoneum  or  serosa  is  thin  and  very 
closely  attached.  In  places  where  the  peritoneum  is  freely  movable,  a 
considerable  amount  of  loose  connective  tissue,  rich  in  elastic  fibres 
and  containing  varying  numbers  of  fat  cells,  connects  the  peritoneum 
with  the  underlying  tissue.  This  is  known  as  the  "subserous  tissue.''' 
The  peritoneum  is  well  supplied  with  blood-vessels  and  lymphatics. 
The  former  give  rise  to  a  rich  capillary  network. 

The  mesentery  is  a  sheet  of  loosely  arranged  connective  tissue  cov- 
ered with  peritoneum.  It  is  reflected  from  the  post-abdominal  wall  to 
the  viscera,  and  serves  to  carry  to  these  organs  their  blood-vessels, 
lymphatics,  and  nerves.  In  the  case  of  the  stomach,  duodenum, 
and  large  intestine,  the  mesentery  is  comparatively  short,  and 
the  organs  are  therefore  ciuite  firmly  fixed  to  the  abdominal  wall. 
In  the  case  of  the  small  intestine  the  mesentery  is  long  and  the  intes- 
tine, therefore,  freely  movable.  The  mesentery  is  richly  supplied 
with  lymph  nodes  and  there  is  usually  a  considerable  amount  of  fat. 
From  the  mesentery,  the  peritoneum  passes  over  to  and  envelops  the 
viscera. 

The  omentum  (Fig.  26)  is  a  sheet  of  tissue  which  passes  from  the 
liver  to  the  lesser  curvature  of  the  stomach  (gastro-hepatic  omentum) 
to  which  it  is  attached,  and  from  the  greater  curvature  of  the  stomach 
to  the  transverse  colon  (greater  omentum).  It  is  similar  in  structure 
to  the  mesentery,  and  contains  usually  much  fat  and  many  lymph  nodes. 
Its  connective-tissue  Ijundles  are  arranged  in  networks,  the  strand  and 
meshes  of  which  vary  greatly  in  size  and  sha])c.  The  strands  are 
covered  by  a  single  layer  of  mesothelium. 


236 


THE  ORGx\NS. 


ElOOD- VESSELS    OF    THE    StOMACH    AND    INTESTINES. 

The  arteries  reach  the  gastro-intestinal  canal  through  the  mesen- 
tery and  pass  through  the  muscular  coats  to  the  submucosa,  where 
they  form  an  extensive  plexus  of  large  vessels  (Heller's  plexus)  (Fig. 
152,  c).  Within  the  muscular  coats  the  main  arteries  give  off  small 
branches  to  the  muscle  tissue.  From  the  plexus  of  the  submucosa 
two  main  sets  of  vessels  arise,  one  passing  outward  to  supply  the  mus- 


FiG.  152. — Scheme  of  B load-vessels  and  Lymphatics  of  Stomach.  X  70.  (Szy- 
monowicz,  after  Mall.)  a,  Mucous  membrane;  h,  muscularis  mucosae;  c,  submucosa;  d, 
inner  circular  muscle  layer;  e,  outer  longitudinal  muscle  layer;  A,  blood-vessels;  B,  structure 
of  coats;  C,  lymphatics. 


cular  coats,  the  other  inward  to  supply  the  mucous  membrane  (Fig. 
152).  Of  the  former  the  larger  vessels  pass  directly  to  the  intermuscu- 
lar septum,  where  they  form  a  plexus  from  which  branches  are  given  off 
to  the  two  muscular  tunics.  A  few  small  branches  from  the  larger 
recurrent  vessels  also  supply  the  inner  muscular  layer.  Of  the  branches 
of  the  submucosa  plexus  which  pass  to  the  mucous  membrane,  the 
shorter  sui>j>ly  the  muscularis  mucostfi,  while  the  longer  branches  pierce 
the  latter  to  form  a  capillary  plexus  among  the  glands  of  the  stroma. 
From  the  capillaries  small  veins  take  origin  which  pierce  the  muscularis 


THE  DIGESTR'E  SYSTEM. 


237 


mucosae  and  form  a  close-meshed  venous  plexus  in  the  submucosa 
(Fig.  152).  These  in  turn  give  rise  to  larger  veins,  which  accompany 
the  arteries  into  the  mesentery. 

In  the  small  intestine  the  distribution  of  the  blood-vessels  is  modified 
by  the  presence  of  the  vilH  (Fig.  153).  Each  villus  receives  one  small 
artery,  or,  in  the  case  of  the  larger  villi,  two  or  three  small  arteries. 


-  A 
i 

i 


Fig.  153. — Scheme  of  Blood-vessels  and  Lymphatics  of  Human  Small  Intestine. 
(From  Bohm  and  von  Davidoff,  after  Mall.)  a,  Central  lacteal  of  villus;  &,  lacteal:  c, 
stroma;  d,  muscularis  mucosae;  e,  submucosa;/,  plexus  of  lymph  vessels;  ^,  circular  muscle 
layer;  h,  plexus  of  lymph  vessels;  /,  longitudinal  muscle  layer;  ],  serous  coat;  k,  vein;  /, 
artery;  m,  base  of  villus;  «,  crypt;  o,  arten,-  of  villus;  />,  vein  of  villus;  q,  epithelium. 


The  artery  passes  through  the  long  axis  of  the  villus  close  under  the 
epithelium  to  its  summit,  giving  off  a  network  of  fine  capillaries,  which 
for  the  most  part  lie  just  beneath  the  epithelium.  From  these,  one  or 
two  small  veins  arise  which  lie  on  the  oposite  side  of  the  villus  from  the 
artery. 

Lymphatics  of  the  Stom.a.ch  .\nd  Intestine. 

Small  lymph   or  chyle  capillaries   begin  as   blind   canals  in  the 
stroma  of  the  mucous  membrane  among  the  tulnilar  glands  (Fig.  152). 


238 


THE  ORGANS. 


In  the  small  intestine  a  lymph  (chyle)  capillary  occupies  the  centre  of 
the  long  axis  of  each  villus,  ending  in  a  blind  extremity  beneath  the 
epithelium  of  its  summit  (Fig.  153).  These  vessels  unite  to  form  a 
narrow-meshed  plexus  of  lymph  capillaries  in  the  deeper  part  of  the 
stroma,  lying  parallel  to  the  muscularis  mucosas.  V'essels  from  this 
plexus  pass  through  the  muscularis  mucosae  and  form  a  wider  meshed 
plexus  of  larger  lymph  vessels  in  the  submucosa.  A  third  lymphatic 
plexus  lies  in  the  connective  tissue  which  separates  the  two  layers  of 
muscle.  From  the  plexus  in  the  submucosa,  branches  pass  through 
the  inner  muscular  layer,  receive  vessels  from  the  intermuscular  plexus, 
and  then  pierce  the  outer  muscular  layer  to  pass  into  the  mesentery  in 
company  with  the  arteries  and  veins. 

Nerves  of  the  Stomach  and  Intestines. 

The  nerves  which  supply  the  stomach  and  intestines  are  mainly 
non-medullated  sympathetic  fibres.  They  reach  the  intestinal  walls 
through  the  mesentery.     In  the  connective  tissue  between  the  two 

layers  of  muscle,  these  fibres 
are  associated  with  groups 
of  sympathetic  ganglion 
cells  to  form  the  plexus 
myentericus  or  plexus  of 
Auerbach.  The  dendrites 
of  the  ganglion  cells  inter- 
lace, forming  a  large  part 
of  the  plexus.  The  axones 
are  grouped  together  in 
small  bundles  of  non-med- 
uUated  fibres,  which  pass 
into  the  muscular  coats, 
where  they  form  intricate 
plexuses,  from  which  are 
given  off  club-shaped  termi- 
nals to  the  smooth  muscle  cells.  From  Auerbach's  plexus  fibres 
pass  to  the  submucosa,  where  they  form  a  similar  but  finer-meshed, 
more  delicate  plexus,  also  associated  with  groups  of  sympathetic  gan- 
glion cells,  the  plexus  of  Meissner.  Both  fibres  and  cells  are  smaller 
than  those  of  Auerbach's  plexus.  From  Meissner's  plexus  delicate 
fibrils  pass  to  their  terminations  in  submucosa,  muscularis  mucosae, 
and  mucous  membrane. 


Fig.  154. — Section  through  Glands  of  Fundus  of 
Hunaan  Stomach  in  Condition  of  Hunger.  X  500. 
(Bohm  and  von  Davidoff.)  a,  Stroma;  b,  parietal 
cell;  c,  lumen;  d,  chief  cell. 


the  digestive  system.  239 

Secretion  and  Absorption. 

The  secretory  activities  of  epithelial  cells  have  already  been  men- 
tioned (page  i86).  The  epithelium  of  the  gastro-intestina!  tract  must 
be  considered  as  ha^•ing  two  main  functions:  (i)  The  secretion  of 
substances  necessary  to  digestion;  and  (2)  the  absorption  of  the  products 
of  digestion. 

I  (i)  Secretion. — The  production  of  mucus  takes  place  in  the 
mucous  or  goblet  cell,  which,  as  already  mentioned,  probably  represents 
a  differentiation  of  the  ordinary  columnar  epithelial  cell.     The  chief 


i^^'i  :m/'} 


""^V, 


/^ ,  /  »§« 


Fig.  155. — Section  through  Glands  of  Fundus  of  Human  Stomach  during  Digestion 
X  500.     (Bohm  and  von  Davidoff.)       a,  Lumen;  b,  stroma;  c,  chief  cell;  d,  parietal  cell 

cells,  "peptic  cells,"  of  the  stomach  glands  are  large  and  clear  during 
fasting,  become  granular  and  cloudy  with  the  onset  of  digestion, 
and  smaller  with  loss  of  granules  during  the  digestive  process.  As 
activity  of  the  chief  cells  (Fig.  155)  is  coincident  with  an  increase  in  the 
pepsin  found  in  the  gastric  mucosa,  it  is  probable  that  these  cells  pro- 
duce pepsin,  and  that  the  granules  represent  some  stage  in  the  elabor- 
ation of  the  ferment.  As  their  name  of  "acid  cells"  would  indicate, 
the  parietal  cells  were  considered  the  source  of  the  liydrocliloric  acid 
of  the  stomach.  While  doubt  still  exists  as  to  the  function  of  these 
cells,  recent  investigations  make  it  probable  that  it  is  not  the  secretion 
of  hydrochloric  acid.  The  cells  of  Brunner's  glands  undergo  changes 
during  digestion,  which  are  quite  similar  to  those  described  as  occurring 
in  the  chief  cells  of  the  stomach  glands,  and  are  probablv  also  con- 


240  THE  ORGANS. 

cerned  in  the  production  of  pepsin.  The  only  function  of  the  intestinal 
crypts  which  has  yet  been  determined  is  the  secretion  of  mucus.  The 
possibility  that  certain  cells  of  the  crypts  of  the  small  intestine  produce 
a  specific  secretion  has  been  mentioned  (page  228). 


A 


.1-^-^^^^Q.J 


O      CD        { 


O 
'^0 


-^ 


1  ;  O     O  " 

r  I  ^ 

O     0    >'--- 

O  ^ 

^^  ^^  o  o 


:---    ^ 


O    pi.' 

u 


Fig.  156. — Fat  Absorption.  Longitudinal  section  of  villus  of  cat's  small  intestine, 
three  hours  after  feeding.  X  350.  Osmic  acid,  a,  Fat  droplets  in  epithelial  cells;  b,  fat 
droplets  in  leucocytes  in  stroma;  c,  fat  droplets  in  leucocytes  within  lacteal;  d,  fat  droplets 
free  in  lacteal;  e,  capillary  containing  blood  cells;/,  central  lacteal  of  villus. 

(2)  Absorption  of  Fat. — While  various  other  products  of  diges- 
tion are  aljsorbcd  l)y  the  intestine,  the  absorption  of  fat  is  the  one  most 
easily  observed.  After  feeding  fat,  fatty  acids,  or  soaps,  fat  globules 
are  found  to  have  penetrated  the  intestinal  mucosa,  and  may  be  seen  in 
(a)  the  epithelial  cells,  (b)  the  leucocytes,  and  (c)  the  lacteals  of  the  villi 
(Fig.  156).  Fat  globules  are  never  seen  in  the  thickened  free  borders 
of  the  cells.    Hence  it  seems  probable  that  the  fat  before  passing  through 


THE  DIGESTR'E  SYSTEM.  241 

this  part  of  the  cell  becomes  split  up  into  glycerin  and  fatty  acids  which 
are  united  again  to  form  fat  within  the  protoplasm  of  the  cell.  Leuco- 
cytes containing  fat  globules  are  seen  throughout  the  stroma.  Within 
the  lacteals  are  found  fat-containing  leucocytes  and  free  fat  droplets 
of  various  size.  It  would  thus  seem  probable  that  the  process  of  fat 
absorption  consists  in:  (i)  The  passage  of  glycerin  and  fatty  acids 
through  the  cell  borders;  (2)  their  reunion  in  the  cell  to  form  fat;  (3) 
the  transference  of  these, fat  globules  to  leucocytes;  which  (4)  carry  them 
to  the  lacteals.  In  the  lacteals  the  fat  is  probably  set  free  by  disinte- 
gration of  the  leucocytes. 

TECHNIC. 

(i)  The  technic  for  the  small  and  large  intestines  and  rectum  is  the  same  as  for 
the  stomach.  Accurate  fixation  of  the  vilH  is  difficult,  there  being  usually  some 
shrinkage  of  the  connective  tissue  of  the  core  away  from  the  epithelium. 

A  longitudinal  section  should  be  made  through  the  junction  of  small  and  large 
intestine,  showing  the  transition  from  the  villus-covered  surface  of  the  former  to 
the  comparatively  smooth  surface  of  the  latter. 

To  show  Brunner's  glands  a  section  of  the  duodenum  is  required. 

To  show  the  varying  shapes  of  the  villi  in  the  different  regions,  sections  should 
also  be  made  of  the  jejunum  and  ileum. 

Solitary  follicles  may  usually  be  seen  in  any  of  the  above  sections. 

A  small  Peyer's  patch,  together  with  the  entire  thickness  of  the  intestinal  wall, 
should  be  removed,  treated  as  above,  stained  with  haematoxylin-eosin  (technic  i, 
p.  18),  or  with  hasmatoxylin-picro-acid-fuchsin  (technic  3,  p.  19),  and  mounted  in 
balsam. 

(2)  A  vermiform  appendix,  as  fresh  as  possible,  should  be  cut  transversely  into 
small  pieces,  fixed  in  formalin-AIuller's  fluid  (technic  5,  p.  7),  and  hardened  in 
alcohol.  Thin  transverse  sections  are  made  through  the  entire  wall,  stained  with 
haematoxylin-eosin  or  hasmatoxylin-picro-acid-fuchsin,  and  mounted  in  balsam. 

(3)  Fat  Absorption. — For  the  purpose  of  studying  the  process  by  which  fat 
passes  from  the  lumen  of  the  gut  into  the  chvle  vessels,  an  animal  should  be  killed 
at  the  height  of  fat  absorption.  A  frog  fed  with  fat  bacon  and  killed  two  days 
later,  a  dog  fed  with  fat  meat,  or  a  cat  with  cream  and  killed  after  from  four  to 
eight  hours,  furnishes  good  material.  Usually  if  the  preparation  is  to  be  successful, 
the  lumen  of  the  intestine  will  be  found  to  contain  emulsified  fat  and  the  lacteals  of 
the  mesentery  are  seen  distended  with  chyle.  Extremely  thin  slices  of  the  mucous 
membrane  of  the  small  intestine  are  fixed  in  i-per-cent.  osmic  acid  or  in  osmium 
bichromate  solution  (5-per-cent.  aqueous  solution  potassium  bichromate  and  2-per- 
cent, aqueous  solution  osmic  acid — equal  parts)  for  twelve  to  twenty-four  hours, 
after  which  they  are  passed  rather  quickly  through  graded  alcohols.  Sections 
should  be  ihin  and  mounted,  either  unstained  or  alter  a  slight  eosin  stain,  in 
glycerin. 

(4)  The  blood-vessels  of  the  stomach  arc  best  studied  in  injected  specimens. 
(See  page  22.) 

16 


242  THE  ORGANS. 

The  Larger  Glands  of  the  Digestive  System. 

The  smaller  tubular  glands  which  form  a  part  of  the  mucous  mem- 
brane and  submucosa  of  the  alimentary  tract  have  been  already  de- 
scribed. Certain  larger  glandular  structures,  the  development  of 
which  is  similar  to  that  of  the  smaller  tubules  but  which  come  to  lie 
wholly  without  the  alimentary  tract,  connected  with  it  only  by  their 
main  excretory  ducts,  and  which  are  yet  functionally  an  important 
part  of  the  digestive  system,  remain  to  be  considered. 

These  are: 

r  (a)  The  parotid. 

1.  The  salivary  glands    -l  {b)  The  sublingual. 

(  (c)  The  submaxillary. 

2.  The  pancreas. 

3.  The  liver. 

The  Salivary  Glands. 

The  salivary  glands  are  all  compound  tubular  glands.  In  man 
the  parotid  is  serous;  the  sublingual  and  submaxillary,  mixed  serous 
and  mucous  (page  194).  Only  the  general  structure  of  these  glands 
is  here  described,  the  minute  structure  of  mucous  and  serous  glands 
having  been  described  on  page  194. 

Each  gland  consists  of  gland  tissue  proper  and  of  a  supporting 
connective-tissue  framework.  The  framework  consists  of  a  connect- 
ive-tissue capsule  which  encloses  the  gland,  but  blends  externally 
with  and  attaches  the  gland  to  the  surrounding  structures.  From 
the  capsule  trabeculce  pass  into  the  gland,  subdividing  it  into  lobes 
and  lobules.  The  gland  tissue  proper  consists  of  systems  of  excretory 
duels  opening  into  secretory  tubules,  all  being  lined  with  one  or  more 
layers  of  epithelial  cells.  Each  gland  has  one  main  excretory  duct. 
This  divides  into  branches — interlobar  ducts — which  run  to  the  lobes 
in  the  connective  tissue  which  separates  them.  The  interlobar  ducts 
give  rise  to  branches  which,  as  they  pass  to  the  lobules  in  the  inter- 
lobular connective  tissue,  are  known  as  interlobular  ducts.  From 
the  latter,  branches  enter  the  lobules — intralobular  ducts — and  split 
up  into  terminal  secreting  tubules  which  constitute  the  bulk  of  the  lobule. 
As  the  smaller  inlrahjbular  ducts  are  lined  with  cells  of  a  secretory 
type,  and  probably  take  part  in  the  elaboration  of  the  secretion  of  the 
gland,  they  ha\'e  been  called  salivary  or  secreting  tubules.  These,  in 
the  submaxillary  and  ])ar()tid  glands,  o])cn  into  tubules  which  have  a 


THE  DIGESTR'E  SYSTEM. 


24.3 


narrow  lumen  and  are  lined  with  low  or  flat  epithelium;  lying  between 
the  secreting  tubules  and  the  terminal  tubules,  they  are  known  as 
intercalated  or  intermediate  tubules.  From  the  interlobular  connective 
tissue  delicate  extensions  pass  into  the  lobules,  separating  the  gland 
tubules.  The  glandular  tissue  is  known  as  thQ  parenchyma  of  the  gland 
in  contradistinction  to  the  connecti\e  or  interstitial  tissue. 

The  parotid  gland  in  man,  dog,  cat,  and  rabbit  is  a  purely  serous 
gland.  Its  duct  system  is  complex.  The  main  excretory  duct 
(Stenoni)  is  lined  by  two  layers  of  columnar  epithelium  resting  upon  a 


(«ei 


(^,    r-i 


Fig.  157. — Diagrams  to  illustrate  the  Structure  of  the  Salivarj-  Glands.  (Stohr.) 
.1,  Parotid;  B,  sublingual;  C,  submaxillary,  a,  Excretory  duct;  b,  secreting  tubule;  c, 
intermediate  tubule;  d,  terminal  tubule. 


distinct  basement  membrane.  The  main  duct  divides  into  numerous 
branches,  which  in  turn  gi\'e  rise  to  the  'secreting  or  salivary  tubules. 
These  are  continuous  with  the  long  narrow  intermediate  tubules,  from 
each  of  which  are  given  ofT  a  number  of  short  terminal  tubules  (Figs.  157, 
A  and  158).  The  two-layered  epithelium  of  the  main  duct  becomes  re- 
duced in  the  smaller  ducts  to  a  single  layer  of  columnar  cells.  The  sali- 
vary tubules  are  lined  with  high  columnar  epithelium,  the  bases  of  the 
cells  showing  distinct  longitudinal  striations.  In  the  intermediate  tubule 
the  epithelium  is  flat,  sometimes  spindle-shaped.  The  terminal 
tubules  are  lined  with  serous  cells  (page  194).  The  connecti\-e  tissue 
usually  contains  a  considerable  number  of  fat  cells. 

The  sublingual  gland  is  a  mixed  gland  in  man,  dog,  cat,  and 


244  THE  ORGANS. 

rabbit.  The  duct  system  is  less  complex  than  in  the  parotid.  The 
main  duct  (Bartholini)  sends  off  branches  which  are  continuous  with 
tubules,  showing  a  few  secretory  mucous  cells.  These  open  directly 
into  the  terminal  tubules  which  art  convoluted  and  vary  greatly  in 
diameter  (Fig.  157,  5).  The  excretory  duct  is  like  that  of  the  parotid 
gland,  lined  with  a  two-layered  columnar  epithelium  resting  upon  a 
basement  membrane.  In  the  smaller  ducts  the  epithelium  is  reduced 
to  a  single  layer  of  columnar  cells.     There  are  no  intermediate  tubules. 


~  Intercalated 
tubule 


Fat  cells    Terminal  tubule 


Fig.  158. — Section  of  Human  Parotid  Gland.      X  252  (Stohr).     The  narrow  lumina 
of  the  terminal  tubules  do  not  sho  v  in  this  figure. 

The  terminal  tubules  are  lined  with  both  serous  and  mucous  cells 
(page  194).  The  crescents  of  Gianuzzi  (page  195)  are  numerous  and 
large.  The  connective  tissue  of  the  gland  contains  many  lymphoid 
cells  (Tig  159J. 

Near  the  sublingual  gland  is  a  group  of  some  5  to  20  simple  tubular 
glands.  Their  terminal  tubules  are  lined  almost  wholly  with  mucous 
cells.  This  grou]>  of  tubules  has  been  designated  the  "sublingualis 
minor." 

The  submaxillary  gland  is  also  a  mixed  gland  in  man,  dog,  cat, 
and  rabbit.  In  complexity  of  its  duct  system  it  stands  between  the 
parotid  and  the  sublingual  (Fig.  157).  The  main  duct  (Wharton's) 
has  not  only  a  two-layered  epithelial  lining  resting  upon  a  basement 


THE   DIGEST  RE  SYSTEM. 


245 


membrane,  but  is  distinguished  by  a  richly  cellular  stroma  and  a  thin 
layer  of  longitudinally  disposed  smooth  muscle.  Branches  of  the 
main  duct  open  into  long  secreting  tubules  which  communicate  with  the 
terminal  tubules  by  means  of  short  narrow  intermediate  tubules  (Fig. 
157,  C).  The  secretory  tubules  are  lined  as  in  the  parotid  with  colum- 
nar cells  whose  bases  are  longitudinally  striated.  These  cells  usually 
contain  more  or  less  yellow  pigment.  The  intermediate  tubules  have  a 
low    cuboidal  or  fiat  epithelium.     Most  of  the  end  tubules  contain 


y 


r%^ 


^^  ©1 


Fig.  159. — Section  of  Human  Sublingual  Gland.  X  252.  (Stohr).  a,  E.xcretory 
duct;  b,  lumina  of  serous  and  mucous  tubules;  c,  mucous  tubule:  (/.demilune;  e,  serous 
tubule;  /,  cross  section  mucous  tubule;  g,  interstitial  connective  tissue. 


serous  cells  only  (page  194).  The  crescents  of  the  mucous  tubules 
(page  195)  are  less  numerous  and  smaller  than  those  in  the  sublingual, 
consisting  as  a  rule  of  only  from  one  to  three  cells  (Fig.  160). 

Blood-vessels. — The  larger  arteries  run  in  the  connective-tissue 
septa  with  the  ducts,  gi\'ing  off  branches  which  accompany  the  di\'isions 
of  the  ducts  to  the  lobules,  where  they  break  up  into  capillary  networks 
among  the  tubules.  These  gi\e  rise  to  \"eins  wliich  accompany  the 
arteries. 

The  lymphatics  Ijegin  as  minute  capillaries  in  the  connective 
tissue  separating  the  terminal  tubules.  These  empty  into  larger 
lymph  vessels  which  accompany  the  arteries  in  the  septa. 


246 


THE  ORGANS. 


The  nerves  of  the  saHvary  glands  are  derived  from  both  cerebro- 
spinal and  sympathetic  systems,  and  consist  of  both  medullated  and 
non-medullated  fibres.  The  medullated  fibres  are  afferent,  probably 
the  dendrites  of  cells  located  in  the  geniculate  gangHon.  Small 
bundles  of  these  fibres  accompany  the  ducts.  Single  fibres  leave  the 
bundles,  lose  their  medullary  sheaths,  and  form  a  non-medullated 
subepithelial  plexus,  from  which  delicate  fibrils  pass  to  end  freely 
among  the  epithehal  cells.  Efferent  impulses  reach  the  gland  through 
the  sympathetic.     The  fibres  are  axones  of  cells  situated  in  small 


Fig.  i6o. — Section  of  Human  Submaxillary  Gland.  X  252.  (Stohr.)  a,  Mucous 
tubule;  b,  serous  tubule;  c,  intermediate  tubule;  (/,  "secretory"  tubule;  e,  demilune;/, 
lumen;  g,  interstitial  connective  tissue. 


peripheral  ganglia;  the  cells  sending  axones  to  the  submaxillary  lying 
upon  the  main  excretory  duct  and  some  of  its  larger  branches;  those 
sending  axones  to  the  sublingual  being  situated  in  a  small  ganglion — • 
the  sublingual — lying  in  the  triangular  area  bounded  by  the  chorda 
tymjjani,  the  lingual  nerve,  and  Wharton's  duct;  those  supplying  the 
parotid  probably  being  in  the  otic  ganglion.  Axones  from  these  cells 
enter  the  glands  with  the  excretory  duct  and  follow  its  branchings  to 
the  terminal  tubules,  where  they  form  plexuses  beneath  the  epithelium. 
From  these,  terminals  pass  to  the  secreting  cells.  It  is  probable  that 
the  salivary  glands  also  receive  sym})athetic  fibres  from  cells  of  the 
superior  cervical  ganglia. 


THE  DIGESTR'E  SYSTEM.  247 

TECHNIC. 

(i)  The  salivary  glands  should  be  fixed  in  Flemming's  fluid  (technic  7,  p.  7), 
or  in  formalin-Miiller's  fluid  (technic  5,  p.  7).  Sections  are  cut  as  thin  as  possible, 
stained  with  hasmatoxyhn-eosin  (technic  i,  p.  18),  and  mounted  in  balsam. 

(2)  For  the  study  of  the  secretory  activities  of  the  gland  cells,  glands  from  a 
fasting  animal  should  first  be  examined  and  then  compared  with  those  of  a  gland 
the  secretion  of  which  has  been  stimulated  by  the  subcutaneous  injection  of  pilo- 
carpine. Fix  in  Flemming's  or  in  Zenker's  fluid  (technic  9,  p.  8).  Examine  some 
sections  unstained  and  mounted  in  glycerin,  others  stained  with  hasmatoxylin-eosin 
and  mounted  in  balsam. 

(3)  The  finer  intercellular  and  intracellular  secretory  tubules  are  demon- 
strated by  Golgi's  method.  Small  pieces  of  absolutely  fresh  gland  are  placed  for 
three  days  in  osmium-bichromxate  solution  (3-per-cent.  potassium  bichromate  solu- 
tion, 4  volumes;  i-per-cent.  osmic  acid,  i  volume),  and  then  transferred  without 
washing  to  a  o .  75-per-cent.  aqueous  solution  of  silver  nitrate.  Here  they  remain 
for  from  two  to  four  days,  the  solution  being  frequently  changed.  The  processes 
of  dehydrating  and  embedding  should  be  rapidly  done,  and  sections  mounted  in 
glycerin,  or,  after  clearing  in  xylol,  in  hard  balsam. 

Pancreas. 

The  pancreas  is  a  compound  tubular  gland.  While  in  general 
similar  to  the  salivary  glands,  it  has  a  somewhat  more  complicated 
structure.  A  connective-tissue  capsule  surrounds  the  gland  and  gives 
off  trabeculae  which  pass  into  the  organ  and  divide  it  into  lobules. 

In  some  of  the  lower  animals,  as  for  example  the  cat,  these  lobules 
are  well  defined,  being  completely  separated  from  one  another  by  con- 
necti\'e  tissue.  In  this  respect  they  resemble  the  lobules  of  the  pig's 
liver.  A  number  of  these  primary  lobules  are  grouped  together  and 
surrounded  by  connective  tissue,  which  is  considerably  broader  and 
looser  in  structure  than  that  separating  the  primary  lobules.  These 
constitute  a  lobule  group  or  secondary  lobule. 

In  the  human  pancreas  the  division  into  lobules  and  lobule  groups 
is  much  less  distinct,  although  it  can  usually  be  made  out.  This  is 
due  to  the  incompleteness  of  the  connccti\-e-tissue  septa,  the  human 
pancreas  in  this  respect  resembling  the  human  li\cr.  Rarch-  tlie 
human  pancreas  is  distinctly  lobulatcd. 

The  gland  has  a  main  excretory  duct,  the  pancreatic  duct  or  duct 
of  Wirsung.  In  many  cases  there  is  also  a  secmidary  excretory  duct,  the 
accessory  pancreatic  duct  or  duct  of  Santorini.  Both  open  into  the 
duodenum.  The  main  duct  extends  almost  the  entire  length  of  the 
gland,  giving  off  short  lateral  branches,  one  of  which  enters  the  centre 
of  each  lobule  group.     Here  it  sphts  up  into  branches  which  ])ass  to  the 


248 


THE  ORGANS. 


primary  lobules.  From  these  intralobular  ducts  are  given  off  long, 
narrow,  intermediate  tubules,  which  in  turn  give  rise  to  the  terminal 
secreting  tubules  (Fig.  i6i). 

The  excretory  ducts  are  lined  with  a  simple  high  columnar  epithelium 
which  rests  upon  a  basement  membrane.  Outside  of  this  is  a  connect- 
ive-tissue coat,  the  thickness  of  which  is 
directly  proportionate  to  the  size  of  the  duct. 
In  the  pancreatic  duct  goblet  cells  are  present, 
and  the  accompanying  connective  tissue  of 
the  main  duct  and  of  its  larger  branches 
contains  small  mucous  glands.  As  the  ducts 
decrease  in  size,  the  epithelium  becomes  lower 
until  the  intermediate  tubule  is  reached  where 
it  becomes  fiat. 

The  terminal  tubules  themselves  are  most 
of  them  very  short,  frequently  almost  spherical. 
This  and  the  fact  that  several  terminal  tubules 
are  given  off  from  the  end  of  each  intermedi- 
ate tubule  have  led  to  the  description  of  these 
tubules  as  alveoli,  and  of  the  pancreas  as  a 
tubulo- alveolar  gland,  although  there  is  no 
dilatation  of  the  lumen.  The  terminal  tubules 
are  lined  with  an  irregularly  conical  epithelium 
resting  upon  a  basement  membrane  (Figs. 
162  and  163).  The  appearance  of  these  cells 
depends  upon  their  functional  condition.  Each 
cell  consists  of  a  central  zone  bordering  the 
lumen,  which  contains  numerous  granules  known  as  zymogen  granules, 
and  of  a  peripheral  zone  next  to  the  basement  membrane,  which  is 
homogeneous  and  contains  the  nucleus  (Fig.  163).  The  zymogen 
granules  are  quite  large  granules  and  as  they  are  highly  refractive 
stand  out  distinctly  even  in  the  fresh,  unstained  condition  and  under 
low  magnification.  The  relative  size  of  these  zones  depends  upon 
whether  the  cell  is  in  the  active  or  resting  state  (compare  Fig.  164,  A 
and  B).  During  rest  (fasting)  the  two  zones  are  of  about  equal 
size.  During  the  early  stages  of  activity  (intestinal  digestion)  the 
granules  largely  disappear  and  the  clear  zone  occupies  almost  the 
entire  cell.  During  the  height  of  digestion  the  granules  arc  increased 
in  number  to  such  an  extent  that  they  almost  fill  the  cell,  while 
after  prolonged   secretion  they  are   again  almost   absent.     The   cell 


Fig.  161. — Diagram  to  illus- 
trate Structure  of  Pancreas. 
(Stohr.)  a,  Excretory  duct; 
h,  intermediate  tubule;  c,c, 
terminal  tubules. 


THE  DIGESTIVE  SYSTEM. 


249 


now  returns  to  the  resting  state  in  whicli  the  two  zones  are  about 
equal.  The  increase  and  disappearance  of  the  granules  are  marked 
by  the  appearance  of  the  fluid  secretion  of  the  gland  in  the  lumen. 


Fig.  162. — Section  of  Human  Pancreas.  X  112.  (KoUiker.)  av.  Alveoli;  a,  inter- 
lobular duct  surrounded  by  interlobular  connective  tissue;  L,  islands  of  Langerhans;  v, 
small  vein. 

It   would    thus   seem   probable   that   the   zymogen   granules   are    the 
Intracellular  representatives  of  the  secretion  of  the  gland. 

In  sections  of  the  gland  there  are  seen  within  the  lumina  of  many 
of  the  secreting  tubules  one  or  more  small  cells  of  which  little  but  the 
nucleus  can  usually  be  made 
out.  These  cells  lie  in  contact 
with  the  secreting  cells,  and 
resemble  the  flat  cells  which 
line  the  intermediate  tubule. 
They  are  known  as  the  centro- 
acinar  {centro-iiihidar)  cells  of 
Langerhans  (Fig.  163,  f).  Their 
significance  is  not  definitely 
known.      Langerhans  believed  "  ,      '-.it.— 

that     they     were     derived    from     p^^     la^.-From   Section   of  Human  Pancreas. 

X  700.  (Koiliker.)  a,  Gland  cell;  b,  base- 
ment membrane;  s,  intermediate  tubule;  <r, 
centroacinar  cells;    sk.   intracellular  secretorv 


tubule. 


the     intermediate    tubule,    the 

epithelium    of    which,    instead 

of  directly  joining  that  of  the 

terminal   tubule   as   in   the   submaxillar)-   gland 

into  the  lumen  of  the  terminal  tubule  (Fig.  163 

has  been  quite  generally  accepted. 


was   continued    o\er 
This  interpretation 


250 


THE  ORGANS. 


Cells  which  differ  from  the  secreting  cells  are  frequently  found 
wedged  in  between  the  latter.  They  extend  from  the  lumen  to  the 
basement  membrane  and  are  probably  susteniacular. 


Fig.  164. — Sections  of  Alveoli  from  Rabbit's  Pancreas.  (Foster,  after  Kuhne  and  Lea.) 
.4,  Resting  alveolus, , the  inner  zone  (a),  containing  zymogen  granules,  occupying  a  little 
more  of  the  cell  than  the  outer  clear  zone  (h) ;  c,  indistinct  lumen.  B,  Active  alveolus, 
granules  coarser,  fewer,  and  confined  to  inner  ends  of  the  cell  (a),  the  outer  clear  zone  (fc) 
being  much  larger;  outlines  of  cells  and  of  lumen  much  more  distinct. 

Passing  from  the  lumen  of  the  terminal  tubule,  sometimes  between 
the  centro-tubular  cells,  directly  into  the  cytoplasm  of  the  secreting 
cells  are  minute  intracellular  secretory  tubules.  These  are  demonstrable 
only  by  special  methods  (Golgi)  (Fig.  165). 


^  B 

Fig.  165. — .Sections  through  Alveoli  of  Human  Pancreas — Golgi  Method — (Dogiel), 
to  show  intracellular  secretory  tubules,  a,  Intermediate  tubule  giving  off  several  terminal 
tubules,  from  which  pass  off  minute  intracellular  secretory  lubulcs;  h,  gland  cells  lining 
terminal  tubules. 

I'he  pancreas  also  contains  pecuHar  groups  of  cells,  the  cell-islands 
of Langerhans ,  having  a  diameter  from  200  to  300//.  (Figs.  162,  166,  and 
167).  The  "island"  cells  differ  quite  markedly  both  in  arrangement 
and  structure  from  those  which  line  the   terminal  tubules  (P'ig.  166). 


THE  UIGESTR'E  SYSTEM.  251 

They  contain  no  zymogen  granules.  They  are  arranged  in  anas- 
tomosing cords  or  strands  which  are  separated  from  one  another  by 
capillaries.  There  are  no  ducts  and  the  method  of  Golgi  shows  no 
inter-  or  intra-cellular  secretory  tubules.  Their  protoplasm  is  un- 
stained by  basic  dyes,  but  stains  homogeneously  with  acid  dyes.  Their 
nuclei  vary  greatly  in  size,  some,  especially  where  the  cells  are  closely 

a 
I 


A; 


[>;:»#-5  O   O,  ^?  c  >' 


:©To' 


©    U^^CfC;..>'ir 


6 

Fig.  1 66. — Island  of  Langerhans  and  few  surrounding  Pancreatic  Tubules.     (Bohm  and 
von  Davidoff.)      a,  Capillary;  b,  tubule. 

packed,  being  small,  others  being  large  and  vesicular.  Some  of  the 
islands  are  quite  sharply  outlined  by  delicate  fibrils  of  connective 
tissue  containing  a  few  elastic  fibres  (Fig.  i66).  Others  blend  with 
the  surrounding  tissues. 

The  origin,  structure,  and  function  of  these  islands  have  been  subjects  of  much 
controversy.  For  some  time  they  were  considered  of  lymphoid  origin.  They  are 
now  believed  to  be  epithelial  cells  having  a  developmental  history  similar  to  the 
cells  lining  the  secreting  tubules.  Each  cell-island  consists  of,  in  addition  to  the 
cells,  a  tuft  or  glomerulus  of  broad  tortuous  anastomosing  capillaries,  which  arise 
from  the  network  of  capillaries  which  surround  the  secreting  tubules.  The  close 
relation  of  cells  and  capillaries  and  the  absence  of  any  ducts  have  led  to  the  hy- 
pothesis that  these  cells  furnish  a  secretion — mtcr>ial  secretion — which  passes 
directly  into  the  blood-vessels. 

In  a  recent  publication  Opie  reviews  previous  work  upon  the  histology  of  the 
pancreas  and  adds  the  results  of  his  own  careful  researches.     He  concludes  that  the 


9n0 


THE  ORGANS. 


cell-islands  of  Langerhans  are  definite  structures  "formed  in  embryological  life," 
that  ''they  possess  an  anatomical  identity  as  definite  as  the  glomeruli  of  the  kidney 
or  the  Malpighian  body  of  the  spleen,  and  that  they  subserve  some  special  function." 
He  calls  attention  to  the  similarity  which  Schafer  noted  between  these  cell-islands 
and  such  small  ductless  structures  as  the  carotid  and  coccygeal  glands  and  the 
parathyreoid  bodies.  From  his  study  of  the  pancreas  in  diabetes,  Opie  concludes 
that  the  islands  of  Langerhans  are  concerned  in  carbohydrate  metabolism. 


Fig.  167. — From  SecUon  of  Pancreas,  the  blood-vessels  of  which  had  been  injected 
(Kiihne  and  Lea),  showing  island  of  Langerhans  with  injected  blood-vessels,  surrounded 
by  sections  of  tubules.     Zymogen  granules  are  distinct  in  inner  ends  of  cells. 

Blood-vessels. — The  arteries  enter  the  pancreas  with  the  main 
duct  and  break  up  into  smaller  arteries  which  accompany  the  smaller 
ducts.  These  end  in  a  capillary  network  among  the  secreting  tubules. 
From  this,  venous  radicles  arise  which  converge  to  form  larger  veins. 
These  pass  out  of  the  gland  in  company  with  the  arteries. 

Lymphatics. — Of  the  lymphatics  little  is  known. 

Nerves. — The  nerves  are  almost  wholly  from  the  sympathetic 
system,  and  are  non-medullated.  Some  of  them  are  axones  of  cells  in 
sympathetic  ganglia,  outside  the  pancreas;  others,  of  cells  situated  in 
small  ganglia  within  the  substance  of  the  gland.  They  pass  to  plexuses 
among  the  secreting  tubules,  to  which  and  to  the  walls  of  the  vessels 
they  send  delicate  terminal  fibrils. 

TECHNIC. 

(i)  The  general  technic  for  the  pancreas  is  the  same  as  for  the  salivary  glands 
(page  247). 

(2)  Zymogen  granules  may  be  demonstrated  by  fixation  in  formalin-Mliller's 
fluid  (technic  5,  p.  7),  and  staining  with  picro-acid-fuchsin  (technic  2,  p.  18),  or  with 
Heidenhain's  iron  hfematoxylin  (technic  3,  p.  16). 

(3)  The  arrangement  of  the  blood-vessels  in  the  i.slands  of  Langerhans  may  be 
studied  in  specimens  in  which  the  vascular  system  has  been  injected  (page  22). 


THE  DIGESTR'E  SYSTEM. 


253 


The  Liver. 

The  liver  is  a  compound  tubular  gland,  the  secreting  tubules  of 
which  anastomose.  There  are  thus,  strictly  speaking,  no  "terminal 
tubules"  in  the  liver,  the  lumina  and  walls  of  neighboring  tubules 
anastomosing  without  any  distinct  line  of  demarcation. 

The  li\'er  is  surrounded  by  a  connective-tissue  capsule,  the  capsule 
of  Glisson.  At  the  hilum  this  capsule  extends  deep  into  the  substance 
of  the  liver,  gi^'ing  off  broad  connective-tissue  septa,  which  di\'ide  the 


Fig.  i68 — Section  of  Lobule  of  Pig's  Liver  X  60  (technic  i,  p.  261),  showing  lobule 
completely  surrounded  by  connective  tissue,  a,  Portal  vein;  b,  bile  duct;  c,  hepatic  artery; 
d,  portal  canal;  e,  capillaries;/,  central  vein;  g,  cords  of  liver  cells;  h,  hepatic  vein. 


organ  into  lobes.  From  the  capsule  and  from  these  interlobar  septa, 
trabeculas  pass  into  the  lobes,  subdi\iding  them  into  lobules.  In  some 
animals,  as  for  example  the  pig,  each  lobule  is  completely  invested  by 
connective  tissue  (Fig.  i68).  In  man,  only  islands  of  connective 
tissue  are  found,  usually  at  points  where  three  or  more  lobules  meet 
(Fig.  169).  The  lobules  are  cylindrical  or  irregularly  polyhedral  in 
shape,  about  i  mm.  in  I^rcadth  and  2  mm.  in  length.  Excepting  just 
beneath  the  capsule,  wlicrc  they  arc  fre(|uent]y  arranged  with  their 


254 


THE  ORGANS. 


apices    toward    the    surface,    the    Kver    lobules    have    an    irregular 
arrangement. 

The  lobule  (Fig.  i68)  which  may  be  considered  the  anatomic  unit 
of  structure  of  the  liver,  consists  of  secreting  tubules  arranged  in  a 
definite  manner  relatively  to  the  blood-vessels.  The  blood-vessels 
of  the  liver  must  therefore  be  first  considered. 


Ik 


'^':7^>^^ 


i*^"'* 

^'^'= 


P     K 


./:  -•.• 


*'(   'v",  ' 


-^  ^ 


,    i', 

>a  I, 


-¥, 


>wv:i 


S   P   H 


Fig.  169. — Section  of  Human  Liver.  X  80.  (Hendrickson.)  P,  Portal  vein;  H, 
hepatic  artery;  B,  bile  duct.  P,  H,  B  constitute  the  portal  canal  and  lie  in  the  connective 
tissue  between  the  lobules. 


The  BLOOD  SUPPLY  of  the  liver  is  peculiar  in  that  in  addition  to 
the  ordinary  arterial  supply  and  venous  return,  which  all  organs 
possess,  the  liver  receives  venous  blood  in  large  quantities  through  the 
portal  vein.  There  are  thus  two  afferent  vessels,  the  hepatic  artery 
and  the  portal  vein,  the  former  carrying  arterial  blood,  the  latter  venous 
blood  from  the  intestine.  ]3oth  vessels  enter  the  liver  at  the  hilum 
and  divide  into  large  interlobar  branches,  which  follow  the  connective- 
tissue  septa  between  the  lobes.  From  these  are  given  off  interlobular 
branches,  which  run  in  the  smaller  connective-tissue  septa  between  the 


THE  DIGESTR'E  SYSTEM. 


lobules.  From  the  interlobular  branches  of  the  portal  vein  arise  veins 
which  are  still  interlobular  and  encircle  the  lobules.  These  send  off 
short  branches  which  pass  to  the  surface  of  the  lobule,  where  they 
break  up  into  a  rich  intralobular  capillary  network.  These  intralobular 
capillaries  all  converge  toward  the  centre  of  the  lobule,  where  they 
empty  into  the  central  vein  (Fig.  i68).  The  central  ^■eins  are  the 
smallest  radicles  of  the  hepatic  veins, 
which  are  the  efferent  vessels  of  the  liver. 
Each  central  vein  begins  at  the  apex  of 
the  lobule  as  a  small  vessel  little  larger 
than  a  capillary.  As  it  passes  through 
the  centre  of  the  long  axis  of  the  lobule 
the  central  vein  constantly  receives  capil- 
laries from  all  sides,  and,  increasing  in 
size,  leaves  the  lobule  at  its  base.  Here 
it  unites  with  the  central  veins  of  other 
lobules  to  form  the  sublohular  vein  which 
is  a  branch  of  the  hepatic  (Fig.  176). 

The  hepatic  artery  accompanies  the 
portal  vein,  following  the  branchings  of 
the  latter  through  the  interlobar  and  inter- 
lobular connective  tissue,  where  its  finer 
twigs  break  up  into  capillary  networks. 
Some  of  these  capillaries  empty  into  the 
smaller  branches  of  the  portal  vein;  others 
enter  the  lobules  and  anastomose  with 
the  intralobular  portal  capillaries. 

The  M.A.IN  EXCRETORY  DUCT — hepatic  duct — leaves  the  liver  at  the 
hilum  near  the  entrance  of  the  portal  \-ein  and  hepatic  artery.  Within 
the  liver  the  duct  di\ides  and  subdivides,  giving  off  interlobar,  and 
these  in  turn  interlobular  branches.  These  ramify  in  the  connective 
tissue,  where  they  always  accompany  the  branches  of  the  portal  vein 
and  hepatic  artery.  These  three  structures— the  hepatic  artery,  the 
portal  vein,  and  the  bile  duct,  which  always  occur  together  in  the 
connective  tissue  which  marks  the  point  of  separation  of  three  or  more 
lobules — together  constitute  the  portal  canal  (Fig.  170).  From  the 
interlobular  ducts  short  branches  pass  to  the  surfaces  of  the  lobules. 
From  these  are  given  oft"  extremely  narrow  tubules,  which  enter  the 
lobule  as  intralobular  secreting  tubules. 

The  walls  of  the  ducts  consist  of  a  single  layer  of  epithelial  cells 


Fig.   170. 


Portal  Canal.  X315. 
(Klein  and  Smith.)  a,  Hepatic 
artery;  1',  portal  vein;  6,  bile 
duct. 


256  THE  ORGANS. 

resting  upon  a  basement  membrane  and  surrounded  by  connective 
tissue  (Fig.  170).  The  height  of  the  epithelium  and  the  amount  of 
connective  tissue  are  directly  proportionate  to  the  size  of  the  duct. 
In  the  largest  ducts  there  are  usually  a  few  scattered  smooth  muscle 
cells.  The  walls  of  the  secreting  tubules  are  formed  by  the  liver  cells. 
The  LIVER  CELLS  (Fig.  171)  are  irregularly  polyhedral  in  shape. 
They  have  a  granular  protoplasm  which  frequently  contains  glycogen, 
pigment  granules,  and  droplets  of  fat  and  bile.     Each  cell  contains 


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Fig.  171. — Part  of  Lobule  of  Human  Liver,  showing  capillaries  and  anastomosing  cords  of 
liver  cells.      X  350.     a,  Liver  cells;  b,  capillaries. 


one  or  more  spherical  nuclei.  Like  other  gland  cells,  the  granularity 
of  the  protoplasm  depends  upon  its  functional  condition.  Within 
the  cells  arc  minute  irregular  canals,  some  of  which  can  be  injected 
through  the  blood-vessels,  while  others  are  apparently  continuous 
with  the  secreting  tubules  (Fig.  173,  A  and  B). 

The  capillaries  of  the  portal  vein,  as  they  anastomose  and  converge 
from  the  periphery  to  the  centre  of  the  lobule,  form  long-meshed  capil- 
lary networks.  In  the  meshes  of  this  network  lie  the  anastomosing 
secreting  tubules.  On  account  of  the  shape  of  the  capillary  network, 
the  liver  cells,  which  form  the  walls  of  these  tubules,  are  arranged  in 


THE  DIGESTI\-E  SYSTEM. 


257 


anastomosing  rows  or  cords,  known  as  hepatic  cords  or  cords  of  liver 
cells  (Fig.  171). 

The  secreting  tubules  (Fig.  172)  are  extremely  minute  channels, 
the  walls  of  which  are  the  liver  cells.     A  secretory  tubule  always  runs 


Fig.  172. — Part  of  Lobule  of  Human  Liver,  Golgi  Method  (technic  3,  p.  261),  to  show 
relations  of  bile  duct  to  intralobular  secretory  tubules  and  of  the  latter  to  the  liver  cells. 
a,  Bile  duct;  b,  cords  of  liver  cells;  c,  blood  capillaries;  d,  central  vein;  e,  secretory  tubules. 

between  two  contiguous  liver  cells,  in  each  of  which  a  groove  is  formed. 
The  hlood  capillaries,  on  the  other  hand,  are  found  at  the  corners  where 
three  or  more  liver  cells  come  in  contact.  It  thus  results  that  bile 
tubules  and  blood  capillaries  rarely  lie  in  contact,  but  are  regularly 


A  B 

Fig.    173. — A,   Cell  from   human   liver  showing   intracellular  canals   (Browicz);  r, 
intracellular  canal;  n,  nucleus.     B,  From  section  of  rabbit's  liver  injected  through  portal 
vein,    showing   intracellular   canals    (continuous   with    intercellular   blood    capillaries). 
(Schiifer.) 

separated  by  part  of  a  liver  cell.  Exceptions  to  this  rule  sometimes 
occur.  While  most  of  the  secretory  tubules  anastomose,  some  of  them 
end  blindly  either  between  the  liver  cells  or,  in  some  instances,  after 
extending  a  short  distance  within  the  cell  protoplasm  (Fig.  173,  A). 
17 


258 


THE  ORGANS. 


At  the  surface  of  the  lobule  there  is  a  modification  of  some  of  the  liver 
cells  to  a  low  cuboidal  type,  and  these  become  continuous  with  the 
lining  cells  of  the  smallest  bile  ducts,  the  secretory  tubule  being  con- 
tinuous with  the  duct  lumen. 

Special  methods  of  technic  have  demonstrated  a  connective-tissue 
framework  within  the  lobule.  This  consists  of  a  reticulum  of  ex- 
tremely delicate  fibrils  which  envelop  the  capillary  blood-vessels,  and 
of  a  smaller  number  of  coarser  fibres  which  radiate  from  the  region 
of  the  central  ^'ein — radiate  fibres  (Fig.  174). 


Fig.  174. — Liver  Lobule,  to  show  Connective-tissue  Framework.     (Mall.) 


Special  technical  methods  also  show  the  presence  of  stellate  cells 
— cells  of  Kupfi'er — within  the  lobule.  These  are  interpreted  by 
Kupffer  as  belonging  to  the  endothelium  of  the  intralobular  capillaries. 

Comparing  the  liver  with  other  compound  tubular  glands,  it  is  seen 
to  present  certain  marked  peculiarities  which  distinguish  it  and  which 
make  its  structure  as  a  compound  tubular  gland  difficult  to  understand. 
The  most  important  of  these  are  the  following:   (Figs.  175  and  176). 

The  extremely  small  amount  of  connective  tissue;  in  the  human 
liver  not  enough  interlobular  connective  tissue  to  outline  the  lobules, 


THE  DIGESTIVE  SYSTEM. 


259 


while  intralobular  connective  tissue  demonstrable  by  ordinary  staining 
methods  is  wholly  absent.  There  is  thus  no  connective  tissue  seen 
separating  the  cells  of  one  tubule  from  those  of  another  as,  for  example, 
in  such  a  gland  as  the  submaxillary.  The  result  is  that  cells  of  neigh- 
boring tubules  lie  side  by  side,  and  back  to  back  as  it  were,  with  no 
intervening  connective  tissue. 

The  fact  that  unlike  the  tubules  of  other  glands,  the  liver  tubule 
consists  of  only  two  rows  of  cells,  between  which  lies  the  lumen.  The 
latter  is  thus  ne\'er  in  touch  with  more  than  two  cells. 


Fig.  175 


Fig.  175. — Scheme  of  an  Ordinary  Compound  Tubular  Gland.  In  lobule  3  only  the 
ramifications  of  the  excretory  duct,  without  endpieces,  are  shown.  (Stohr).  a,  Branches 
of  excretory  duct;  b,  artery;  c,  vein;  d,  terminal  tubules;  e,  capillaries. 

Fig.  176. — Scheme  of  Liver.  In  lobule  i,  only  the  direction  of  the  endpieces  is  shown; 
in  lobule  2  only  their  branching;  in  3  only  the  excretory  ducts.  (Stohr.)  a,  Branches  of 
excretory  duct;  b,  portal  vein;  c,  terminal  tubules  (hepatic  cords);  d,  capillaries;  e,  vein 
(central  and  sublobular). 


The  cnd'to-cnd  anastomosis  of  the  sccreti)ig  tubules,  there  being 
no  true  terminal  tubules;  anastomosis  of  neighboring  tubules  by  means 
of  side  branches;  the  arrangement  of  the  bile  capillaries  in  such  a  manner 
that  a  single  liver  cell  abuts  upon  more  than  one  capillary. 

TJw  more  intimate  relation  of  the  liver  cell  to  the  blood  capillaries. 
Thus  most  gland  cells  have  one  side  on  the  lumen,  one  side  only  in 
contact  with  a  capillary  blood-vessel,  the  remaining  sides  being  in 
contact  with  other  cells  of  the  same   tubule.     A  liver  cell,  on   the 


260  THE  ORGANS. 

Other  hand,  may  and  usually  does  come  in  contact  with  several  blood 
capillaries. 

The  arrangement  of  hath  blood-vessels  and  tubules  ivithin  the 
lobule.  In  the  submaxillary,  for  example,  the  terminal  tubules  are 
convoluted  and  run  in  all  directions.  In  the  liver  the  terminal  tubules 
are  straight  and  run  in  a  definite  direction  from  the  periphery  of  the 
lobule  toward  the  center.  Again,  while  in  other  glands  both  intra- 
lobular arteries  and  ducts  are  distributed  outward  from  the  centre  of 
the  lobule,  and  the  blood  is  returned  through  veins  which  pass  to 
the  periphery  of  the  lobule,  in  the  liver  the  interlobular  ducts  pass  to 
the  periphery  of  the  lobule  and  give  off  secreting  tubules  which  pass 
in  toward  the  centre  of  the  lobule.  The  afferent  vessels  also  (portal 
veins)  take  the  blood  to  the  periphery  of  the  lobule  and  distribute 
it  to  a  capillary  network  which  converges  to  an  efferent  vessel  (hepatic 
vein)  at  the  centre  of  the  lobule.  The  veins  are  also  peculiar  in  that 
they  do  not  follow  the  arteries  in  leaving  the  liver  but  pursue  an  en- 
tirely independent  course. 

Blood-vessels. — These  have  been  already  described. 

Lymph  vessels  form  a  network  in  the  liver  capsule.  These  com- 
municate with  deep  lymphatics  in  the  substance  of  the  organ.  The 
latter  accompany  the  portal  vein  and  follow  the  ramifications  of  its 
capillaries  within  the  lobule  as  far  as  the  central  vein. 

The  nerves  of  the  liver  are  mainly  non-medullated  axones  of 
sympathetic  neurones.  The  nerves  accompany  the  blood-vessels  and 
bile  ducts,  around  which  they  form  plexuses.  These  plexuses  give 
off  fibrils  which  end  on  the  blood-vessels,  bile  ducts,  and  liver  cells. 

Three  main  ducts,  all  parts  of  a  single  excretory  duct  system,  are 
concerned  in  the  transportation  of  the  bile  to  the  intestine,  the  hepatic, 
the  cystic,  and  the  common.  Their  walls  consist  of  a  mucous  membrane, 
a  submucosa,  and  a  layer  of  smooth  muscle.  The  mucosa  is  composed 
of  a  simple  columnar  epithelium  resting  upon  a  basement  membrane 
and  a  stroma  which  contains  smooth  muscle  cells  and  small  mucous 
glands.  The  submucosa  is  a  thin  layer  of  connective  tissue.  Hen- 
drickson  describes  the  muscular  coat  as  consisting  of  three  layers,  an 
inner  circular,  a  middle  longitudinal,  and  an  external  oblique.  At  the 
entrance  of  the  common  bile  duct  into  the  intestine,  and  at  the  junction 
of  the  duct  of  Wirsung  with  the  common  duct,  there  are  thickenings 
of  the  circular  fibres  to  form  sphincters.  In  the  cystic  duct  occur 
folds  of  the  mucosa — the  Heisterian  valve — into  which  the  muscularis 
extends. 


THE  DIGESTIVE  SYSTEM.  261 

The  Gail-Bladder. 

The  wall  of  the  gall-bladder  consists  of  three  coats— mucous, 
muscular,  and  serous. 

The  mucous  membrane  is  thrown  up  into  small  folds  or  ruga, 
which  anastomose  and  give  the  mucous  surface  a  reticular  appearance. 
The  epithelium  is  of  the  simple  columnar  variety  with  nuclei  situated 
at  the  basal  ends  of  the  cells.  A  few  mucous  glands  are  usually  found 
in  the  stroma. 

The  muscular  coat  consists  of  bundles  of  smooth  muscle  cells 
which  are  disposed  in  a  very  irregular  manner,  and  are  separated  by 
considerable  fibrous  tissue.  A  richly  vascular  layer  just  beneath  the 
stroma  is  almost  free  from  muscle  and  corresponds  to  a  submucosa. 
It  frec[uently  contains  small  lymph  nodules. 

The  serous  coat  is  a  reflection  of  the  peritoneum. 

TECHNIC. 

(i)  Before  taking  up  the  study  of  the  human  liver,  the  liver  from  one  of  the 
'lower  animals  in  Avhich  each  lobule  is  completely  surrounded  by  connective  tissue 
should  be  studied.  Fix  small  pieces  of  a  pig's  liver  in  formalin-Miiller's  fluid 
(technic  5,  p.  7.)  Cut  sections  near  and  parallel  to  the  surface.  Stain  with  hsem- 
ato.xylin-picro-acid-fuchsin  (technic  3,  p.  19)  and  mount  in  balsam.  In  the  pig's 
liver  the  lobules  are  completely  outlined  by  connective  tissue  and  the  yellow  picric- 
acid-stained  lobules  are  in  sharp  contrast  with  the  red  fuchsin-stained  connective 
tissue. 

(2)  For  the  study  of  the  human  liver  treat  small  pieces  of  perfectly  fresh  tissue 
in  the  same  manner  as  the  preceding,  but  stain  with  haematoxylin-eosin  (technic  i, 
p.  18). 

(3)  The  secretory  tubules  and  smaller  bile  ducts  may  be  demonstrated  by  tech- 
nic 4,  p.  26.     A  light  eosin  stain  brings  out  the  liver  cells 

(4)  For  the  study  of  the  blood-vessels  of  the  Uver,  inject  the  vessels  through 
the  inferior  vena  cava  or  portal  vein.  If  the  vena  cava  is  used,  it  is  convenient  to 
inject  from  the  heart  directly  through  the  right  auricle  into  the  vena  cava.  Sec- 
tions should  be  rather  thick  and  may  be  stained  with  eosin,  or  even  lightly  with 
hajmatoxylin-eosin  (technic  i,  p.  18),  and  mounted  in  balsam. 

(5)  For  demonstrating  the  intralobular  connective  tissue,  Oppel  recommends 
fixing  fresh  tissue  in  alcohol,  placing  for  twenty-four  hours  in  a  0.5-per-cent.  aqueous 
solution  of  yellow  chromate  of  potassium,  washing  in  very  dilute  silver  nitrate 
solution  (a  few  drops  of  o.  75-per-cent.  solution  to  50  c.c.  of  water)  and  then  trans- 
ferring to  o.  75-per-cent.  silver  nitrate  solution,  where  it  remains  for  twenty-four 
hours.  Embed  quickly  in  celloidin.  The  best  tissue  is  usually  found  near  the 
surfaces  of  the  blocks.  A  similar  result  is  obtained  by  fixing  fresh  tissue  in  0.5- 
per-cent.  chromic-acid  solution  for  three  days,  then  transferring  to  0.5-per-cent. 
silver  nitrate  solution  for  two  davs. 


262  the  organs. 

Development  of  the  Digestive  System. 

In  the  development  of  the  digestive  system  all  the  layers  of  the 
blastoderm  are  involved.  Mesoderm  and  entoderm  are,  however,  the 
layers  most  concerned,  as  the  ectoderm  is  used  only  in  the  formation 
of  the  oral  and  anal  orifices.  The  primitive  alimentary  canal  is  formed 
by  two  folds  which  grow  out  from  the  ventral  surface  of  the  embryo 
and  unite  to  form  a  canal,  in  a  manner  that  is  quite  similar  to  the 
formation  of  the  neural  canal.  In  this  way  the  primitive  gut  is  lined 
with  cells  which  previously  formed  the  ventral  surface  of  the  embryo, 
i.e.,  entoderm.  A  portion  of  the  mesoderm  accompanies  the  entoderm 
in  the  formation  of  the  folds.  This  is  known  as  the  visceral  layer  of 
the  mesoderm.  The  primary  gut  is  thus  a  closed  sac  or  tube.  It  is 
connected  with  the  umbilical  vesicle,  but  has  no  connection  with  the 
exterior.  These  connections  are  formed  later  by  oral  and  anal  invagi- 
nations of  ectoderm  which  extend  inward  and  open  up  into  the  ends 
of  the  hitherto  imperforate  gut.  The  ends  of  the  alimentary  tract, 
including  the  oral  cavity  and  all  of  the  glands  and  other  structures 
connected  with  it,  are  of  ectodermic  origin.  The  epitheHal  lining 
of  the  gut  and  the  parenchyma  of  all  glands  connected  with  it  are 
derived  from  entoderm.  The  muscle,  the  connective  tissue,  and  the 
mesothelium  of  the  serosa  are  developed  from  mesoderm. 

The  mesodermic  elements  show  little  variation  throughout  the  gut, 
the  peculiarities  of  the  several  anatomical  divisions  of  the  latter  being 
dependent  mainly  on  special  differentiation  of  the  entoderm  (epithe- 
lium). Beneath  the  entodermic  cells  is  a  narrow  layer  of  loosely 
arranged  tissue  which  later  separates  into  stroma,  muscularis  mucosae, 
and  submucosa.  Outside  of  this  a  broader  mesodermic  band  of  firmer 
structure  represents  the  future  muscularis. 

The  stomach  first  appears  as  a  spindle-shaped  dilatation  about  the 
end  of  the  first  month.  Its  entodermic  cells,  which  had  consisted  of 
a  single  layer,  increase  in  number  and  arrange  themselves  in  short 
cylindrical  groups.  These  are  the  first  traces  of  tubular  glands. 
They  increase  in  length  and  extend  downward  into  the  mesodermic 
tissue.  For  a  time  the  cells  lining  the  peptic  glands  are  all  apparently 
alike,  but  at  about  the  fourth  month  the  differentiation  into  chief  cells 
and  parietal  cells  takes  place. 

In  the  intestines  a  proliferation  of  the  epithelium  and  of  the  under- 
lying stroma  results  in  the  formation  of  villi.  These  appear  about 
the  tenth  week,  in  both  small  and  large  intestines.     In  the  former 


THE  DIGESTIVE  SYSTEM.  263 

they  increase  in  size,  while  in  the  latter  they  atrophy  and  ultimately 
disappear.  The  simple  tubular  glands  of  the  intestines  develop  in  a 
manner  similar  to  those  of  the  stomach. 

The  mesothelium  of  the  serosa  is  derived  from  the  mesodermic 
cells  of  the  primitive  body  cavity. 

The  development  of  the  larger  glands,  connected  with  the  digesti^•e 
tract,  takes  place  in  a  manner  similar  to  the  formation  of  the  simple 
tubular  glands.  All  originate  in  extensions  downward  of  entodermic 
cords  into  the  underlying  mesodermic  tissue.  From  the  lower  ends 
of  these  cords,  branches  extend  in  all  directions  to  form  the  complex 
systems  of  tubules  found  in  the  compound  glands. 

The  salivary  glands  being  developed  from  the  oral  ca^•ity,  originate 
in  similar  invaginations  of  ectodermic  tissue. 

In  the  case  of  the  pancreas  a  portion  of  the  gland  has  an  independent 
origin  in  the  epithelium  of  the  ductus  choledochus.  This  portion 
ultimately  unites  with  the  main  mass  of  the  gland  and  its  duct.  The 
duct  of  Santorini  sometimes  remains  patent,  but  in  many  cases  atrophies 
so  that  the  entire  pancreatic  secretion  usually  reaches  the  intestine 
through  the  pancreatic  duct. 

The  liver  begins  as  a  ventral  downgrowth  of  the  intestinal  epithe- 
lium into  the  mesoderm  of  the  transverse  septum.  This  almost 
immediately  divides  into  two  hepatic  diverticula.  About  the  ends  of 
these  diverticula  active  proliferation  of  entodermic  cells  takes  place, 
and  this  represents  the  first  appearance  of  liver  tissue. 

General  References  for  Further  Study. 

Oppel:  Lehrbuch  der  vergleichenden  mikroskopischen  Anatomie. 

Kolliker:  Handbuch  der  Gewebelehre  des  Menschen. 

Opie:  The  Pancreas. 

Stohr:  Salivary  Glands,  in  Te.\t-book  of  Histology- 


CHAPTER  VII. 

THE  RESPIRATORY  SYSTEM. 

The  respiratory  apparatus  consists  of  a  system  of  passages — nares, 
larynx,  trachea,  and  bronchi,  which  serve  for  the  transmission  of  air 
to  and  from  the  essential  organ  of  respiration,  the  lungs. 

The  Nares. 

The  nares,  or  nasal  passages,  are  divided  into  vestibular,  respira- 
tory, and  olfactory  regions,  the  differentiation  depending  mainly  upon 
the  structure  of  their  mucous  membranes. 

The  VESTIBULAR  REGION  marks  the  transition  between  skin  and 
mucous  membrane  (page  193).  Its  epithelium  is  of  the  stratified 
squamous  variety  and  rests  upon  a  basement  membrane,  which  is 
thrown  into  folds  by  papillae  of  the  underlying  stroma.  The  latter  is 
richly  cellular  and  contains  sebaceous  glands  (page  362)  and  the  follicles 
of  the  nasal  hairs. 

The  RESPIRATORY  REGION  is  much  larger  than  both  the  vestibular 
and  olfactory  regions.  Its  epithelium  is  of  the  stratified  columnar 
variety.  The  cells  of  the  surface  layer  are  ciliated  and  are  inter- 
spersed with  goblet  cells.  The  stroma  is  distinguished  by  its  thickness 
(3  to  5  mm.  over  the  inferior  turbinates)  and  by  the  presence  of  net- 
works of  such  large  veins  that  the  tissue  closely  resembles  erectile 
tissue.  It  contains  considerable  diffuse  lymphoid  tissue  and  here  and 
there  small  lymph  nodules.  In  the  stroma  are  small  simple  tubular 
glands  lined  with  both  serous  and  mucous  cells.  There  is  no  sub- 
mucosa,  the  stroma  being  connected  directly  with  the  periosteum  and 
perichondrium  of  the  nasal  bones  and  cartilages. 

The  mucous  membrane  of  the  accessory  nasal  sinuses  is  similar  in 
structure  to  that  of  the  respiratory  region  of  the  nares,  but  is  thinner 
and  contains  fewer  glands. 

The  OLFACTORY  REGION  Can  be  distinguished  with  the  naked  eye 
by  its  brownish-yellow  color,  in  contrast  with  the  reddish  tint  of  the 

264 


THE  RESPIRATORY  SYSTEM.  265 

surrounding  respiratory  mucosa.  The  epithelium  is  of  the  stratified 
columnar  type,  and  is  considerably  thicker  than  that  of  the  respiratory 
region.  The  surface  cells  are  of  two  kinds:  (i)  sustentacular  cells, 
and  (2)  olfactory  cells. 

(i)  The  sustentacular  cells  are  the  more  numerous.  Each  cell 
consists  of  three  parts:  {a)  A  superficial  portion,  which  is  broad  and 
cylindrical,  and  contains  pigment,  and  granules  arranged  in  longi- 
tudinal rows.  The  cells  have  well-marked,  striated,  thickened  free 
borders,  which  unite  to  form  the  so-called  memhrana  limitans  olfactoria. 
(b)  A  middle  portion  which  contains  an  oval  nucleus.  As  the  nuclei 
of  these  cells  all  lie  in  the  same  plane,  they  form  a  distinct  narrow  band, 
which  is  known  as  the  zone  of  oval  nuclei,  (c)  A  thin  filamentous 
process  which  extends  from  the  nuclear  portion  down  between  the  cells 
of  the  deeper  layers.  This  process  is  irregular  and  pitted  by  pressure 
of  surrounding  cells.  It  usually  forks  and  apparently  anastomoses 
with  processes  of  other  cells  to  form  a  sort  of  protoplasmic  reticulum. 

(2)  The  olfactory  cells  lie  between  the  sustentacular  cells.  Their 
nuclei  are  spherical,  lie  at  different  levels,  and  are  most  of  them  more 
deeply  placed  than  those  of  the  sustentacular  cells.  They  thus  form 
a  broad  band,  the  zone  of  round  nuclei.  From  the  nuclear  portion  of 
the  cell  a  delicate  process  extends  to  the  surface,  where  it  ends  in 
several  minute  hair-like  processes.  From  the  opposite  pole  of  the  cell  a 
longer  process  extends  centrally  as  a  centripetal  nerve  fibre.  The 
olfactory  cell  is  thus  seen  to  be  of  the  nature  of  a  ganglion  cell  (see 
also  page  382). 

Between  the  nuclear  parts  of  the  olfactory  cells  and  the  basement 
membrane  are  the  basal  cells.  These  are  small  nucleated  elements, 
the  irregular  branching  protoplasm  of  which  anastomoses  with  that 
of  neighboring  basal  cells  and  of  the  sustentacular  cells  to  form  the 
peculiar  protoplasmic  reticulum  already  mentioned. 

The  basement  membrane  is  not  well  developed. 

The  stroma  consists  of  loosely  arranged  white  fibres,  delicate  elastic 
fibres,  and  connective-tissue  cells.  Embedded  in  the  stroma  are 
large  numbers  of  simple  branched  tubular  glands,  the  glands  of  Bow- 
man. Each  tubule  consists  of  a  duct,  a  body,  and  a  fundus.  The 
secreting  cells  are  large  and  irregular  and  contain  a  yellowish  pigment, 
which  with  that  of  the  sustentacular  cells  is  responsible  for  the  peculiar 
color  of  the  olfactory  mucosa.  These  glands  were  long  described  as 
serous,  but  are  now  ])clie\'ed  to  be  mucous  in  character.  They  fre- 
quently extend  beyond  the  limits  of  the  olfactory  region. 


266  THE  ORGANS. 

The  Larynx. 

The  larynx  consists  essentially  of  a  group  of  cartilages  united  by 
strong  fibrous  bands  and  lined  by  mucous  membrane. 

The  epithelium  covering  the  true  vocal  cords,  the  laryngeal  surface 
of  the  epiglottis,  and  the  anterior  surface  of  the  arytenoid  cartilages  is 
of  the  stratified  squamous  variety  with  underlying  papillae.  With 
these  exceptions  the  mucous  membrane  of  the  larynx  is  lined  with 
stratified  columnar  cihated  epithelium  similar  to  that  of  the  respiratory 
portion  of  the  nares.  Numerous  goblet  cells  are  usually  present,  and 
the  epithelium  rests  upon  a  broad  basement  membrane.  On  the 
posterior  surface  of  the  epiglottis  many  taste  buds  (see  Fig.  268  and 
page  532)  are  embedded  in  the  epithelium. 

The  stroma  is  especially  rich  in  elastic  fibres.  The  true  vocal 
cords  consist  almost  wholly  of  longitudinal  elastic  fibres  covered  by 
stratified  squamous  epithelium.  Lymphoid  cells  are  present  in  vary- 
ing numbers.  In  some  places  they  are  so  numerous  that  the  tissue 
assumes  the  character  of  diffuse  lymphoid  tissue.  Distinct  nodules 
sometimes  occur. 

Owing  to  the  absence  of  a  muscularis  mucosae  the  stroma  passes 
over  with  no  distinct  line  of  demarcation  into  the  submucosa.  This 
is  a  more  loosely  arranged,  less  cellular  connective  tissue,  and  con- 
tains simple  tubular  glands  lined  with  both  serous  and  mucous  cells. 

Externally  the  submucosa  merges  into  a  layer  of  more  dense  fibrous 
tissue  which  connects  it  with  the  laryngeal  cartilages  and  with  the 
surrounding  structures.  Immediately  surrounding  the  cartilages  the 
connective  tissue  forms  an  extremely  dense  layer,  the  perichondrium. 

Of  the  cartilages  of  the  larynx,  the  epiglottis,  the  middle  part  of 
the  thyreoid,  the  apex  and  vocal  process  of  the  arytenoid,  the  carti- 
lages of  Santorini  and  of  Wrisburg  are  of  the  yellow  elastic  variety. 
The  main  body  of  the  arytenoid,  the  rest  of  the  thyreoid  and  the  cricoid 
cartilages  are  hyaline.  After  the  twentieth  year,  more  or  less  ossi- 
fication is  usually  found  in  the  cricoid  and  thyreoid  cartilages. 

The  Trachea. 

I'he  walls  of  the  trachea  consist  of  three  layers — mucosa,  submu- 
cosa, and  fibrosa  (Fig.  177). 

The  mucosa  is  continuous  with  that  of  the  larynx,  which  it  closely 
resembles  in  structure.  It  consists  of  a  stratified  columnar  ciliated 
epithelium,  with  numerous  goblet  cells,  resting  upon  a  broad  base- 


THE  RESPIRATORY  SYSTEM. 


267 


ment  membrane,  and  of  a  stroma  of  mixed  fibrous  and  elastic  tissue 
containing  many  lymphoid  cells. 

The  submucosa  is  not  distinctly  marked  off  from  the  stroma  on 
account  of  the  absence  of  a  muscularis  mucosae.  It  is  distinguished 
from  the  stroma  by  its  looser,  less  cellular  structure,  by  its  numerous 
large  blood-vessels,  and  by  the  presence  of  glands.  These  are  of  the. 
simple  branched  tubular  variety  and  are  lined  with  both  serous  and 
mucous  cells.     Some  of  the  mucous  tubules  have  well-marked  cres- 


.'  -.'1 


-J 


Fig.  177. — From  Longitudinal  Section  of  Human  Trachea.  X  40.  (Technic  3, 
p.  269.)  a,  Epithelium;  b,  stroma;  c,  cartilage;  d,  fibrous  coat;  e,  serous  tubules;  /,  mucous 
tubules;  g,  glands  in  submucosa;  //,  ducts. 

cents  of  Gianuzzi.  The  glands  are  most  numerous  between  the  ends 
of  the  cartilaginous  rings,  where  they  frequently  penetrate  the  muscle 
and  extend  into  the  fibrosa. 

The  fibrosa  is  composed  of  coarse,  rather  loosely  woven  connect- 
ive-tissue fibres  embedded  in  which  are  the  tracheal  cartilages.  These 
are  incomplete  rings  of  hyaline  cartilage  shaped  like  the  letter  C 
(Fig.  178).  They  are  from  sixteen  to  twenty  in  number  and  encircle 
about  four-fifths  of  the  tul)e,  l^eing  open  posteriorly.  The  openings 
between  the  ends  of  the  cartilaginous  rings  are  bridged  over  bv  a 


268 


THE  ORGANS. 


thickened  continuation  of  the  fibrous  coat,  strengthened  by  a  layer  of 
smooth  muscle  (Fig.  178,  m).  The  bundles  of  muscle  cells  run 
mainly  in  a  transverse  direction,  and  extend  across  the  intervals 
between  adjacent  rings  as  well  as  between  their  open  ends.  There 
are  frequently  a  few  bundles  of  obliquely  disposed  cells  and,  most 
external,  some  few  that  run  longitudinally. 


,  __jMsr«=«'^-^=^«=E5B>nj^^ 


Fig.  178. — Transverse  Section  of  Human  Trachea  through  One  (;f  the  Cartilage 
Rings.  X  8.  (KoUiker.)  E,  EpitheHum  of  (s)  mucous  membrane;  dr,  glands;  as,  gland 
duct;  ad,  adenoid  tissue;  K,  cartilage;  ?n,  smooth  muscle  cut  longitudinally,  extending 
across  between  ends  of  cartilage  ring. 


Outside  the  fibrous  coat  proper  is  a  looser,  more  irregular  con- 
nective tissue,  which  serves  to  attach  the  trachea  to  the  surrounding 
structures. 

Blood-vessels,  lymphatics,  and  nerves  have  a  similar  distribution 
in  larynx  and  trachea.  The  larger  vessels  pass  directly  to  the  sub- 
mucosa.  From  these,  smaller  branches  pass  to  the  different  coats, 
where  they  break  u])  into  capillary  networks. 


THE  RESPIRATORY  SYSTEM.  269 

Lymphatics  form  plexuses  in  the  submucosa  and  mucosa,  the  most 
superficial  lying  just  beneath  the  subepithelial  capillary  plexus. 

The  nerves  of  the  larynx  and  trachea  are  derived  from  both  cere- 
bro-spinal  and  sympathetic  systems.  The  cerebro-spinal  nerves  are 
afferent,  the  dendrites  of  spinal  ganglion  cells.  They  form  a  sub- 
epithelial plexus  from  which  are  given  off  fibrils  which  pass  into  the 
epithelium  and  terminate  freely  among  the  epithelial  cells.  Other 
afferent  fibres  of  cerebro-spinal  nerves  pass  to  the  muscular  coat  of 
the  trachea.  Sympathetic  nerve  fibres  form  plexuses  which  are 
interspersed  with  minute  groups  of  ganglion  cells.  Axones  from 
these  ganglion  cells  have  been  traced  to  the  smooth  muscle  cells  of  the 
trachea.  Sympathetic  axones  also  pass  to  the  glands  of  the  trachea 
and  larynx.  On  the  under  surface  of  the  epiglottis  small  taste  buds 
are  found. 

TECHNIC. 

(i)  For  the  study  of  the  details  of  structure  of  the  walls  of  the  nares  and  larynx, 
fix  small  pieces  of  perfectly  fresh  material  from  different  regions  in  formalin-Mlil- 
ler's  fluid  (technic  5,  p.  7),  harden  in  alcohol,  stain  sections  with  hsematoxylin- 
eosin  (technic  i,  p.  18),  and  mount  in  balsam. 

(2)  The  general  relations  of  the  parts  can  be  studied  by  removing  the  larynx, 
upper  part  of  the  trachea,  and  corresponding  portion  of  the  oesophagus  of  an  ani- 
mal or  of  a  new-born  child,  fixing  and  hardening  as  above,  and  cutting  longitudinal 
sections  through  the  entire  specimen. 

(3)  Trachea. — Remove  a  portion  of  the  trachea  and  treat  as  in  technic  (i). 
Both  longitudinal  and  transverse  sections  should  be  made;  the  longitudinal  includ- 
ing at  least  two  of  the  cartilaginous  rings;  the  transverse  being  through  one  of  the 
rings. 

The  Bronchi. 

The  primary  bronchi  and  their  largest  branches  hax'e  essentially 
the  same  structure  as  the  trachea  except  that  the  cartilaginous  rings 
are  not  as  complete.  Bronchi  branch  at  acute  angles  and  also  give 
off  small  side  branches. 

As  they  decrease  in  calibre,  the  following  changes  take  place  in 
their  walls  (Figs.  179  to  182). 

(i)  The  epithelium  gradually  becomes  thinner.  In  a  bronchus 
of  medium  size  (Fig.  179)  it  has  become  reduced  to  three  layers  of  cells, 
which  Kolliker  describes  as  an  outer  "basal"  layer,  a  middle  "replac- 
ing" layer,  and  a  surface  layer  of  ciliated  and  goblet  cells.  In  the 
smaller  bronchi  (Figs.  181, 182)  the  epithelium  is  reduced  to  a  single  layer 


270 


THE  ORGANS. 


of  ciliated  cells.  These  are  at  first  high,  but  become  gradually  lower 
as  the  bronchi  become  smaller,  until  in  the  terminal  branches  the 
epithehum  is  simple  cuboidal  and  non-ciliated.  Among  the  ciliated 
cells  are  varying  numbers  of  mucous  or  goblet  cells. 

(2)  The  stroma  decreases  in  thickness  as  the  bronchi  become 
smaller.  It  consists  of  loosely  arranged  white  and  elastic  fibres.  This 
layer  with  the  epithelium  is  folded  longitudinally  (Fig.  182.)  There 
is  considerable  diffuse  lymphatic  tissue,   and  in  some  places  small 


Fig.  179. — Transverse  Section  through  two  Medium-size  Bronchi  of  the  Human 
Lung.  X  15.  (Technic  2,  p.  280.)  In  the  fibrous  coat  are  seen  the  bronchial  arteries 
and  veins,  a,  Epithelium;  b,  stroma;  c,  muscularis  mucosae;  d,  lung  tissue;  e,  fibrous 
coat;/,  plates  of  cartilage. 

nodules  occur,  over  which  there  may  be  lymphoid  infiltration  of  the 
epithelium  (see  Tonsil,  page  157).  Near  the  root  of  the  lung  many 
small  lymph  nodules  are  found,  which  show  different  degrees  of 
pigmentation. 

(3)  With  decrease  in  thickness  of  the  epithelium  and  of  the  stroma, 
the  thickness  of  the  mucosa  is  maintained  by  the  appearance  of  a 
layer  of  smooth  muscle.  In  the  larger  bronchi  this  is  a  continuous 
layer  of  circularly  disposed  smooth  muscle,  and  lies  just  external  to 
the  stroma,  forming  a  muscularis  mucosae  (Fig.  180).  It  reaches  its 
greatest  thickness  relative  to  the  size  of  the  bronchus  in  the  bronchi  of 
medium  size.  As  the  bronchi  become  smaller  it  becomes  thinner, 
then  discontinuous,  and  in  the  smallest  bronchi  consists  of  only  a  few 
scattered  muscle  cells.  These  continue  into  the  walls  of  the  alveolar 
ducts,  but  are  absent  beyond  this  point. 

(4)  The  submucosa  decreases    in  thickness  with  decrease  in  the 


THE  RESPIRATORY  SYSTEM.  271 

calibre  of  the  bronchi.  It  consists  of  loosely  arranged  connective 
tissue.  Mixed  glands  (Fig.  i8o)  are  present  until  a  diameter  of  about 
I  mm.  is  reached,  when  they  disappear.  They  lie  in  the  submucosa 
and  frequently  extend  through  between  the  cartilage  plates  into  the 
fibrous  coat.  The  ducts  pass  through  the  muscular  coat  and  open  into 
pit-like  depressions  lined  with  a  continuation  of  the  surface  ciliated 
epithelium. 


Muscle  ."      r  "'  ' ''  "'        '  .-■;•. 

Epithelium        Stroma        coat  ':■•  ■  -  —-:r- Alveoli 


■^vii^ 


/^- 


Nerve 


Blood-vessel'  i:^^  '''"■' l-  W-^!^^ 


Cartilage 


Excretory  duct 


Fig.  i8o. — Cross  Section  of  Human  Bronchus  (of  a  child)  of  2  mm.  diameter. 
X  30.     (Stohr.). 


(5)  The  cartilages,  which  in  the  trachea  and  primary  bronchi  form 
nearly  complete  rings,  become  gradually  smaller,  and  finally  break  up 
into  short  disconnected  plates  (Figs.  179  and  180).  They  are  frequently 
fibrocartilage  rather  than  hyaline.  These  plates  decrease  in  size  and 
number,  and  are  absent  after  a  diameter  of  i  mm.  is  reached.  Cartilage 
and  mucous  glands  thus  disappear  at  about  the  same  time,  although  it 
is  common  for  glands  to  extend  over  into  smaller  bronchi  than  do 
the  cartilage  plates. 

The  bronchi  down  to  a  diameter  of  from  1.5  to  i  mm.  are  inter- 
lobular, and  belon<2;  to  the  duct  svstcm  down  to  a  diameter  of  about 


272  THE  ORGANS. 

0.5  mm.  From  the  small  interlobular  bronchi  are  given  off  the  lerminal 

bronchi.  These  are  respiratory  in  character  and  are  described  with  the 
luncjs. 


S.-' 


V^f 


'•I 


■:;\ 


Fig.   181. — Transverse    Section   of   Small   Bronchus   from   Human  Lung.      X  115. 
(Technic  2,  p.  280.)     a,  Stroma;  h,  epithelium;  c,  muscularis  mucosae;  d,  fibrous  coat. 


3^^..  .,-„„. 


'ftp        ^     ->     «*.^    fe*^    //  ----t^vr'''  "^^      •  ■■'     I'/       •      -<■  ■  -'-  ■aa> 'lOft   ^ 


r*v  >:T1' 


Fig.  182. — Transverse  Section  through  small  Bronchus  of  Human  Lung.  (Sobotta.) 
Simple  columnar  ciliated  epithelium;  no  cartilage;  no  glands;  mucosa  folded  longitudi- 
nally; elastic  tissue  stained  with  Weigert's  elastic  tissue  stain. 


In  studying  the  Ijronchi  it  is  convenient  to  arljitrarily  divide  them  into  large, 
medium-sized,  and  small  bronchi. 

Large  bronchi  have  es.sentially  the  same  structure  as  the  trachea  except  for  some- 
what thinner  wails. 

Medium-sized  hronchi  (Fig.   lyg)  have  an  epithelium  about  three  layers  deep, 


THE  RESPIRATORY  SYSTE:\I.  273 

disconnected  plates  of  cartilage,  a  continuous  layer  of  smooth  muscle  disposed  cir- 
cularly as  a  muscularis  mucosae,  tubular  glands. 

Small  bronchi  have  a  single  layer  of  ciliated  epithelium,  a  thinner  muscular  coat, 
no  glands,  and  no  cartilage.     (Figs.  i8i,  182.) 


The  Lungs. 

The  lung  is  built  upon  the  plan  of  a  compound  alveolar  gland,  the 
trachea  and  bronchial  ramifications  corresponding  to  duct  systems,  the 
air  vesicles  to  gland  alveoli. 

The  surface  of  the  lung  is  covered  by  a  serous  membrane — the 
pulmonary  pleura — which  forms  its  capsule,  and  which  at  the  root  of  the 
lunjy,  or  hilum,  is  reflected  upon  the  inner  surface  of  the  chest  wall  as 
the  parietal  pleura.     It  consists  of  fibrillar  connective  tissue  containing 


Fig.  183. — From  Lung  of  an  Ape.  The  bronchi  and  their  dependent  ducts  and 
alveoli  have  been  filled  with  quicksilver.  X  15.  (KoUiker,  after  Schulze.)  b,  Terminal 
bronchus;  a,  alveolar  duct;  /,  alveoli. 

fine  elastic  fibres  which  are  more  numerous  in  the  visceral  than  in  the 
parietal  layer.  From  the  capsule  broad  connective-tissue  sepia  pass 
into  the  organ,  dividing  it  into  lobes.  From  the  capsule  and  interlobar 
septa  are  given  off  smaller  septa,  which  subdivide  the  lobes  into 
lobules. 

The  human  pulmonary  lobule  (Fig.  184)  is  irregularly  pyramidal, 
and  has  a  diameter  of  from  i  to  3  cm.  The  amount  of  interlobular 
connective  tissue  is  so  small  that  no  distinct  separation  into  lobules  can 
usually  be  made  out.  The  pulmonary  lobule  constitutes  the  anatomic 
unit  of  lung  structure  in  the  same  sense  that  the  liver  lobule  constitutes 
the  anatomic  unit  of  that  organ.  The  most  superficial  lobules  are 
arranged  with  their  bases  against  the  pleura.  Elsewhere  in  the  lung 
the  lobules  have  an  irrcu;ular  arrangement. 


274 


THE  ORGANS. 


■JvAJ-" 


The  apex  of  each  lobule  is  the  point  of  entrance  of  a  terminal  or 
respiratory  bronchus  (Figs.  183  and  184)  which  is  about  0.5  mm.  in 
diameter.  From  each  terminal  bronchus  open  from  three  to  six 
narrow  passages — alveolar  passages  or  alveolar  ducts  (Figs.  183,  184  and 
185).  The  alveolar  passages  open  into  wider  chambers— a/i'eo/ar 
sacs  or  infundibula.  The  latter  are  irregularly  pyramidal,  their  bases 
being  directed  away  from  the  alveolar  ducts.  From  the  sides  of  the 
terminal  bronchi,  the  alveolar  ducts,  and  the  alveolar  sacs,  are  given  off 
the  alveoli — air  vesicles  or  air  cells  (Figs.  183  and  185). 


Bronchial  arterv 


Pulmonary  vein 


Pulmonary  artery 


^HL. Respiratory  bronchus 


Pleural  capillaries 


Fig.  184. — Scheme  of  a  Pulmonary  Lobule  and  its  Blood  Supply  (Stohr).     The  two 
main  branches  of  the  pulmonary  vein  are  seen  lying  in  the  interlobular  connective  tissue. 


According  to  Miller  a  further  subdivision  of  the  alveolar  duct  can  be  made.  He 
describes  the  terminal  bronchus  as  about  0.5  mm.  in  diameter,  and  as  opening  into 
from  three  to  six  narrow  tubules,  the  vestibula.  Each  vestibulum  is  about  o .  2  mm. 
in  diameter,  and  opens  into  several  larger,  nearly  spherical  chambers,  the  atria. 
Each  atrium  communicates  with  a  number  of  very  narrow — 0.14  mm. — air-sac 
passages  from  which  open  the  air  sacs.  From  the  latter  are  given  off  on  all  sides 
the  air  cells  or  alveoli.  Alveoli  are  not,  however,  confined  to  the  periphery  of  the 
air  sacs,  but  are  given  off  in  small  numbers  from  the  terminal  bronchus,  and  in 
constantly  increasing  numbers  from  the  alveolar  ducts  and  infundibula. 

The  terminal  bronchus.     The  proximal  portion  of  the  terminal  or 
respiratory  bronchus  is  lined  by  a  simple  columnar  ciliated  epithelium, 


THE  RESPIRATORY  SYSTEM.  275 

resting  upon  a  basement  membrane.  Beneath  this  is  a  richly  elastic 
stroma  containing  bundles  of  circularly  disposed  smooth  muscle  cells. 
The  epithelium  becomes  gradually  lower  and  non-ciliated,  and  near 
the  distal  end  of  the  terminal  bronchus  there  appear  small  groups  or 
islands  of  flat,  non-nucleated  epithelial  cells — respiratory  epithelium. 

The  alveolar  duct.     Here  the  cuboidal  epithelium  is  almost  com- 
pletely replaced  by  the  respiratory.     Beneath  the  epithelium  the  walls 


Pleura 
Alveoli 


Alveolar  sacs  • 


Blood-vessel 


Respiratory  bronchus 


Alveoli 


Small  bronchus 


Fig.    1S5. — Section    of     Cat's    Lung    (Szymonowicz)    surface    lobule;    respiratory 
bronchus  opening  into  alveolar  duct  from  which  are  given  off  two  alveolar  sacs. 


have  a  structure  similar  to  those  of  the  distal  end  of  the  terminal 
bronchus,  consisting  of  delicate  fibro-elastic  tissue  with  scattered 
smooth  muscle  cells.     The  basement  membrane  is  extremely  thin. 

The  alveolar  sac.  The  epithelium  of  the  alveolar  sac  consists  of 
two  kinds  of  cells,  respiratory  cells  and  so-called  "/a'/a/"  cells  (see 
Development,  page  279). 


276 


THE  ORGANS. 


The  respiratory  cells  (Fig.  i86)  are  some  of  them  large,  flat,  non- 
nucleated  plates,  while  others  are  much  smaller,  non-nucleated  ele- 
ments. The  absence  of  nuclei  and  the  extremely  small  amount  of 
intercellular  substance  render  these  cells  quite  invisible  in  sections 
stained  by  the  more  common  methods.  The  cell  boundaries  are  best 
demonstrated  by  means  of  silver  nitrate  (technic  i,  p.  71). 

The  '' fcetaV  cells  are  granular,  nucleated  cells  which  are  scattered 
among  the  respiratory  cells.  Their  position  appears  to  be  less  super- 
ficial than  that  of  the  respiratory  cells,  the  foetal  cells  lying  in  the  meshes 


Fig.  186. — From  Section  of  Cat's  Lung  Stained  with  Silver  Nitrate.  (Klein. )  (Tech- 
nic I,  p.  71.)  Small  bronchus  surrounded  by  alveoli,  in  which  are  seen  both  flat  cells 
(respiratory  epithelium)  and  cuboidal  cells  (foetal  cells). 


of  the  capillary  network,  the  respiratory  cells  covering  the  capillaries. 
In  the  embryonic  lung  and  in  the  lungs  of  a  still-born  child  the  air 
passages  and  alveoli  contain  only  this  type  of  cells,  the  small  flat 
plates  apparently  resulting  from  a  flattening  out  of  the  cuboidal  cells 
due  to  pressure  from  inspiration,  and  the  large  flat  plates  to  union  of  a 
number  of  small  plates. 

The  alveolus  is  similar  in  structure  to  the  alveolar  duct,  its  walls 
consisting  mainly  of  delicate  elastic  fibrils  supporting  respiratory 
and  ffi'tal  cells.  Around  the  opening  of  the  alveolus  the  elastic  fibres 
are  more  numerous,  forming  a  more  or  less  definite  ring.  The  dis- 
position of  elastic  tissue  in  the  wafl  of  the  alveoli  is  undoubtedly  of 
importance   in   determining   the   contraction   and    expansion   of   the 


THE  RESPIRATORY  SYSTEM. 


277 


alveoli  under  varying  conditions  of  pressure.  It  has  been  estimated 
that  on  forced  inspiration  an  alveolus  can  expand  to  three  times  its 
resting  capacity.  Each  alveolus  communicates  not  only  with  its 
alveolar  sac,  alveolar  duct,  or  respiratory  bronchus,  by  means  of  a 
broad  opening,  but  alveoli  are  connected  with  one  another  by  minute  I 
openings  in  their  walls. 

The  iiiteralveolar  connective  tissue,  while  extremely  small  in  amount, 
serves  to  separate  the  alveoli  from  one  another.     Somewhat  thicker 


Fig.  1S7. — Section  Through  Three  Alveoli  of  Human  Lung.  X  235.  Weigerl's 
elastic-tissue  stain  (technic  3,  p.  26)  to  show  arrangement  of  elastic  tissue,  a,  .\lveolus  cut 
through  side  -walls  only;  b,  alveolus  cut  through  side  walls  and  portion  of  bottom  or  top;  c, 
alveolus  in  which  either  the  bottom  or  top  is  included  in  section. 


connective  tissue  separates  the  alveoli  of  one  alveolar  passage  from 
those  of  another.  Still  stronger  connecti\'e-tissue  bands  separate 
adjacent  lobules. 

Blood-vessels. — Two  systems  of  vessels  distribute  blood  to  the 
lungs.  One,  the  hroncJiial  system,  carries  blood  for  the  nutrition  of 
the  lung  tissue.  The  other,  the  much  larger  piihnanary  system,  carries 
blood  for  the  respiratory  function  (Fig.  184). 

The  hroncJiial  artery  and  the  pulmonary  artery  enter  the  lung  at  its 
hilum.  "Within  the  lung  the  vessels  branch,  following  the  branchings 
of  the  bronchi,  which  they  accompany  (Fig.  184).  The  pulmonary 
vessels  are  much  the  larger  and  run  in  the  connective  tissue  outside  the 
bronchial  walls.  The  bronchial  vessels  lie  icilliiii  the  fibrous  coat  of 
the  l)ronchus.     A  section  of  a  bronchus  thus  usuallv  shows  the  large 


278 


THE  ORGANS. 


pulmonary  vessels,  one  on  either  side  of  the  bronchus,  and  two  or 
more  small  bronchial  vessels  in  the  walls  of  the  bronchus  (Fig.  179). 

The  pulmonary  lobule  forms  a  distinct  "blood-vascular  unit."  A 
branch  of  the  pulmonary  artery  enters  the  apex  of  each  lobule  close 
to  the  lobular  bronchus,  and  almost  immediately  breaks  up  into 
branches,  one  of  which  passes  to  each  alveolar  passage   (Fig.  184). 


Fig.  188. — Parts  of  Four  Alveoli  from  Section  of  Injected  Fluman  Lung.  X  200. 
(Technic  5,  p.  280.)  a,  Wall  of  alveolus  seen  on  flat;  c,  same,  but  only  small  part  of 
alveolar  wall  in  plane  of  section;  b,  alveoli  in  which  plane  of  section  includes  only  side  walls; 
alveolar  wall  seen  on  edge. 


From  these  are  given  off  minute  terminal  arterioles  which  pass  to  the 
central  sides  of  the  alveolar  passages  and  alveoli,  where  they  give  rise  to 
a  rich  capillary  network.  This  capillary  network  is  extremely  close- 
meshed,  and  invests  the  alveoli  on  all  sides  (Fig.  188).  Similar 
networks  invest  the  walls  of  the  respiratory  bronchi,  the  alveolar  ducts, 
and  their  alveoli.     All  of  these  capillary  networks  freely  anastomose. 

There  are  thus  interposed  between  the  blood  in  the  capillaries  and 
the  air  in  the  alveoli  only  three  extremely  thin  layers:  (i)  The  thin 
endothelium  of  the  capillary  wall;  (2)  the  single  layer  of  flat  respiratory 
epithelial  plates;  and  (3)  the  delicate  basement  membrane  upon  which 


THE  RESPIRATORY  SYSTEM.  279 

the  respiratory  epithelium  rests  together  with  an  extremely  small 
amount  of  fibrous  and  elastic  tissues  (see  diagram,  Fig.  189). 

The  veins  begin  as  small  radicles,  one  from  the  base  of  each  alve- 
olus (Fig.  184).  These  empty  into  small  veins  at  the  periphery  of  the 
lobule.  These  veins  at  first  run  in  the  interlobular  connective  tissue 
away  from  the  artery  and  bronchus.  Later  they  empty  into  the  large 
pulmonary  trunks  which  accompany  the  bronchi. 

The  bronchial  arteries  break  up  into  capillary  networks  in  the  walls 
of  the  bronchi,  supplying  them  as  far  as  their  respiratory  divisions, 
beyond  which  point  the  capillaries  belong  to  the  pulmonary  system. 


Fig.  189. — Diagram  of  Tissues  Interposed  Between  Blood  and  Air  in  Alveolus,  a 
Respiratory  epithelium;  6,  basement  membrane  and  small  amount  of  fibro-elastic  tissue 
c,  endothelium  of  capillary. 

The  bronchial  arteries  supply  the  walls  of  the  Ijronchi,  the  bronchial 
lymph  nodes,  the  walls  of  the  pulmonary  vessels,  and  the  pulmonary 
pleura.  Of  the  bronchial  capillaries  some  empty  into  the  bronchial 
veins,  others  into  the  pulmonary  veins. 

Lymphatics. — The  lymphatics  of  the  lung  begin  as  small  lymph 
spaces  in  the  interalveolar  connective  tissue.  These  communicate 
with  larger  lymph  channels  in  the  interlobular  septa.  Some  of  these 
empty  into  the  deep  pulmonary  lymphatics,  which  follow  the  pulmo- 
nary vessels  to  the  lymph  glands  at  the  root  of  the  lung.  Others 
empty  into  the  superficial  pulmonary  lymphatics,  which  form  an 
extensive  subpleural  plexus  connected  with  small  subpleural  lymph 
nodes,  whence  by  means  of  several  larger  vessels  the  lymph  is  carried 
to  the  lymph  nodes  at  the  hilum. 

Nerves. — Bundles  of  medullated  and  non-medullated  fibres  accom- 
pany the  bronchial  arteries  and  veins.  Small  sympathetic  ganglia  are 
distributed  along  these  nerves.  The  fibres  form  plexuses  in  the 
fibrous  layer  of  the  bronchi,  from  which  terminals  pass  to  the  muscle 
of  the  bronchi  and  of  the  vessel  walls  and  to  the  mucosa.  Free  end- 
ings upon  the  epithelium  of  bronchi,  air  passages,  and  alveoli  have 
been  described. 

Development  of  the  Respir.a.tory  System. 

The  epithelium  of  the  respiratory  system  develops  from  entoderm, 
the    connective-tissue    elements    from    mesoderm.     The    first    differ- 


280  THE  ORGANS. 

entiation  of  respiratory  system  appears  as  a  dipping  down  of  the 
entoderm  of  the  floor  of  the  primitive  pharynx.  The  tubule  thus 
formed  divides  into  a  larger  and  longer  right  branch,  which  subdivides 
into  three  branches  corresponding  to  the  three  lobes  of  the  future  right 
lunsf,  and  a  smaller  and  shorter  left  branch,  which  subdivides  into 
two  branches  corresponding  to  the  two  lobes  of  the  future  left  lung. 
By  repeated  subdivisions  of  these  tubules  the  entire  bronchial  system 
is  formed.  The  last  to  develop  are  the  respiratory  divisions  of  the 
bronchi  with  their  alveolar  ducts,  alveolar  sacs  and  alveoli.  The 
epithelium  of  the  alveolar  sacs  and  alveoli  is  at  first  entirely  of  the 
fcetal-cell  type,  the  large  flat  respiratory  plates  appearing  only  after 
the  lungs  have  become  inflated.  The  foetal  and  respiratory  cells  of  the 
adult  lung  have  therefore  the  same  embryonic  origin.  During  the 
early  stages  of  lung  development  the  mesodermic  tissue  predominates, 
but  with  the  rapid  growth  of  the  tubules  the  proportion  of  the  two 
changes  until  in  the  adult  lung  the  mesodermic  tissue  becomes  restricted 
to  the  inconspicuous  pulmonary  framework  and  the  blood-vessels. 

TECHNIC. 

(i)  The  technic  for  the  largest  bronchi  is  the  same  as  for  the  trachea  (technic 
3,  p.  269).     The  medium  size  and  small  bronchi  are  studied  in  sections  of  the  lung. 

(2)  Lung  and  Bronchi. — Carefully  remove  the  lungs  and  trachea  (human,  dog, 
or  cat)  and  tie  into  the  trachea  a  cannula  to  which  a  funnel  is  attached.  Distend 
the  lungs  moderately  (pressure  of  two  to  four  inches)  by  pouring  in  formalin-Miil- 
ler's  fluid  (technic  5,  p.  7),  and  then  immerse  the  whole  in  the  same  fixative  for 
twenty-four  hours.  Cut  into  small  blocks,  using  a  very  sharp  razor  so  as  not  to 
squeeze  the  tissue,  harden  in  alcohol,  stain  thin  sections  with  hsematoxylin-eosin 
(technic  i,  p.  18),  and  mount  in  balsam  or  in  eosin-glycerin.  The  larger  bronchi 
are  found  in  sections  near  the  root  of  the  lung.  The  arrangement  of  the  pulmo- 
nary lobules  is  best  seen  in  sections  near  and  horizontal  to  the  surface.  Sections 
perpendicular  to  and  including  the  surface  show  the  pulmonary  pleura. 

(3)  Respiratory  Epithelium  (technic  i,  p.  71). 

(4)  Elastic  Tissue  of  the  Lung  (technic  3,  p.  26). 

(5)  Blood-vessels. — For  the  study  of  the  blood-vessels,  especially  of  the  capil- 
lary networks  of  the  alveoli,  sections  of  injected  lung  should  be  made.  A  fresh 
lung  is  injected  (page  22)  with  blue  gelatin,  through  the  pulmonary  artery.  It  is 
then  hardened  in  alcohol,  embedded  in  celloidin,  and  thick  sections  are  stained 
with  eosin  and  mounted  in  balsam. 

The  Thyreoid. 

The  thyreoid  (Fig.  190)  is  a  ductless  structure  built  upon  the  general 
principle   of  a   compound   alveolar   gland.     There   are   usually   two 


THE  RESPIRATORY  SYSTEM.  281 

lateral  lobes  connected  by  a  narrow  band  of  glandular  tissue,  the 
"isthmus.''  Each  lobe  is  surrounded  by  a  connective-tissue  capsule, 
from  which  septa  pass  into  the  lobe,  subdividing  it  into  lobules.  From 
the  perilobular  connective  tissue  finer  strands  extend  into  the  lobules, 
separating  the  alveoli.  The  latter  are  spherical,  oval,  or  irregular  in 
shape.  They  vary  greatly  in  diameter  (40  to  120a)  and  are  as  a  rule 
non-communicating.  At  birth  most  of  the  alveoli  are  empty,  but  soon 
become  more  or  less  filled  with  a  peculiar  substance  known  as  "colloid." 
The  aheoli  are  lined  with  a  single  or  double  layer  of  cuboidal  epithelial 
cells.     Two  types  of  cells  are  recognized. 


., ,,.      ._^ 

Fig.  iqo. — Section  of  Human  Thyreoid.     Most  of  the  alveoU  contain  colloid. 


One  of  these  is  actively  secreting  colloid  and  is  known  as  a  secret  nig 
or  colloid  cell.  The  other  contains  no  colloid  and  is  known  as  a 
resting  or  reserve  cell.  It  is  probable  that  their  names  indicate  the 
relation  of  these  cells  to  each  other  and  that  the  reserve  cell  ultimately 
becomes  a  colloid-secreting  cell. 

The  colloid  cell  appears  in  some  cases  simply  to  pour  out  its  colloid 
secretion  into  the  lumen,  after  which  it  may  assume  the  character  of  a 
resting  cell;  in  other  cases  the  cell  appears  to  be  completely  trans- 
formed into  colloid,  its  place  being  taken  by  proliferation  of  the  resting 
cells.  In  certain  alveoli  which  are  much  distended  with  colloid  the 
lining  epithelium  is  flattened. 


282 


THE  ORGANS. 


That  the  thyreoid  exerts  a  decided  influence  upon  general  body  metabolism  is 
shown  by  the  symptoms  resulting  from  congenital  absence  of  the  gland  (congenital 
myxoedema  or  cretinism)  and  by  the  effects  of  complete  removal,  the  latter  giving 
rise  to  a  train  of  symptoms  known  as  the  "cachexia  strumipriva." 

The  blood  supply  of  the  thyreoid  is  extremely  rich,  the  vessels 
branching  and  anastomosing  in  the  connective  tissue  and  forming  dense 
capillary  networks  around  the  alveoli. 

Lymphatics  accompany  the  blood-vessels  in  the  connective  tissue. 

Nerves  are  mainly  non-medullated  fibres  which  form  plexuses 
around  the  blood-vessels  and  in  the  connective  tissue  surrounding  the 
alveoli.     Terminals  to  the  secreting  cells  end  in  club-like  dilatations 


Fig.    191. — Section    of   Human   Parathyreoid;    showing    mainly    "clear," 
"  principal",  or  "chief"  cells.     (Pool.) 

against  the  bases  or  between  the  epithelial  cells.  A  few  afferent 
medullated  fibres  are  found  in  the  plexuses  surrounding  the  blood- 
vessels. 

Development. — The  thyreoid  originates  as  a  diverticulum  from 
the  entoderm  of  the  primitive  pharynx.  It  first  appears  in  embryos 
of  3  to  5  mm.  and  grows  ventrally  into  the  mesoderm  of  the  ventral 
wall  of  the  neck.  Here  it  forms  a  mass  which  Hes  transversely  across 
the  neck.     It  is  composed  of  soh"d  cords  of  cells  which  become  hollow 


THE  RESPIRATORY  SYSTEM. 


283 


to  form  the  alveoli  of  the  gland.  At  first  the  gland  is  connected  with 
the  surface  by  the  thyreo-glossal  duct.  This  either  disappears  entirely 
or  is  represented  in  the  adult  by  such  rudimentary  structures  as  the  so- 
called  prehyoid,  suprahyoid,  and  accessory  thyreoid  glands.  The  gland 
at  first  consists  of  solid  cords  of  cells.  Ingrowth  of  connective  tissue 
divides  these  into  groups  or  lobules,  and  at  the  same  time  breaks  up 
the  long  tubules  into  short  segments.  Dilatation  of  the  alveoli  occurs 
with  the  formation  of  colloid. 

The  Parathyreoids. 

These  are  small  ductless  glands  which  usually  lie  upon  the  posterior 
surface  of  the  lateral  lobes  of  the  thvreoid.     There  are  commonlv  two 


Fig.  192. — Section  of  Human  Parathyreoid  showing  groups  of  oxyphile  cells.      (Pool.) 


pairs,  a  superior  and  an  inferior,  on  each  side.  The  number  is,  however, 
subject  to  variation.  Each  gland  is  from  6  to  8  mm.  long,  about  half 
that  in  breadth,  and  2  mm.  thick.  Small  groups  of  cells  having  the 
structure  of  the  parathyreoids  ha\e  been  found  below  the  thyreoid 

and  within  the  thvreoid  and  thvmus. 


284 


THE  ORGANS. 


The  parathyreoid  is  surrounded  by  a  thin  connective-tissue  capsule 
which  sends  a  variable  amount  of  connective  tissue  into  the  gland  as 
septa.  When  the  amount  is  considerable  the  gland  shows  a  sub- 
division into  lobules.  The  stroma  consists  largely  of  reticular  tissue 
and  is  very  vascular.  The  number  and  arrangement  of  the  cells  vary. 
The  gland  may  be  almost  wholly  cellular  with  very  little  connective 
tissue,  the  groups  of  cells  may  be  widely  separated  by  interstitial  tissue, 


Fig.  193. — Section  of  Human  Parathyreoirl,  showinjj  lumina  indicating  tubular 
or  tutjulo-alveolar  structure.    (Pool.) 


or  there  may  be  any  intermediate  condition.  The  cells  are  arranged 
in  irregular  groups  or  cords  (Figs.  191,  192)  sometimes  around  tubules, 
sometimes  having  a  distinctly  alveolar  structure  (Fig.  193);  in  the 
latter  case  colloid  may  be  present  in  the  lumen.  Colloid  has  also 
been  found  between,  and  colloid  and  glycogen  within,  the  cells. 

The  cells  themselves  are  spheroidal,  cuboidal  or  pyramidal,  with 
basal  nuclei.  The  appearance  of  the  cells  varies  sufficiently  to  have 
caused  two  or  three  types  to  be  distinguished.  All,  however,  probably 
represent  different  functional  conditions  of  the  same  cell,  (i)  Chief  or 
clear  cells  (Fig.  191).     These  are  the  more  numerous.     Their  bodies  are 


THE  RESPIRATORY  SYSTE^E  285 

small  and  clear,  and  the  cytoplasm  does  not  stain  readily.  The  nuclei  are 
large  in  proportion  to  the  cell  and  are  clear  and  vesicular  with  loosely 
arranged  pale  chromatin  network.  ( 2 )  Oxyphile  cells  (Fig.  192 ).  These  ' 
are  larger,  their  cytoplasm  is  more  granular  and  takes  a  strong  eosin  stain. 
The  nucleus  is  small,  its  chromatin  network  closely  arranged  and  takes 
a  dark  stain.  Compact  groups  of  these  cells  occur  especially  just 
beneath  the  capsule.  They  are  also  found  throughout  the  gland, 
arranged  as  cords,  as  single  cells,  or  as  small  groups  among  the  clear 
cells.  Intermediate  types  have  been  described.  It  is  probable  that 
the  clear  cells  represent  the  resting,  the  granular  cells  the  active 
secreting  condition  of  the  same  cell. 

The  parathyreoids  originate  as  epithelial  evaginations  from  the 
third  and  fourth  branchial  grooves,  and  develop  wholly  independently 
of  the  thyreoid. 

The  powerful  influence  which  these  minute  organs  exert  is  shown  both  clinically 
and  experimentally.  Fatal  tetany,  resulting  from  the  earlier  operations  for  complete 
removal  of  the  thyreoids,  has  been  shown  by  animal  experimentation  to  be  due  not 
to  the  removal  of  the  thyreoids,  but  to  coincident  removal  of  the  parathyreoids, 
the  removal  of  the  latter  only,  in  animals,  giving  the  same  results.* 

TECHNIC. 

The  thyreoid  and  parathyreoid  glands  are  best  fixed  in  formalin-Miiller's  fluid. 
Sections  may  be  stained  with  haematoxylin-eosin  or  ha;matoxylin-picro-acid-fuchsin 
and  mounted  in  balsam. 

General  References  for  Further  Study. 

Miller,  W.  S.:  Das  Lungenlappchen,  seine  Blut-  und  Lymphgefasse. 

Councilman:  The  Lobule  of  the  Lung  and  its  Relations  to  the  Lymphatics. 

Kolliker:  Handbuch  der  Gewebelehre  des  Menschen. 

Pool:  Tetany  Parathyreopriva.     Annals  of  Surgery,  October,  1907. 

*  For  much  of  the  description  of  the  parathyreoids  and  for  the  photograph  the  writer  is 
indebted  to  Dr.  Eugene  H.  Pool. 


Ax 


> 


CHAPTER  Vni. 
THE  URINARY  SYSTEM. 

The  Kidney. 

The  kidney  is  a  compound  tubular  gland.  It  is  enclosed  by  a 
firm  connective-tissue  capsule,  the  inner  layer  of  which  contains 
smooth  muscle  cells.     In  many  of  the  lower  animals  and  in  the  human 

foetus  septa  extend  from  the  cap- 
sule into  the  gland,  dividing  it 
into  a  number  of  lobes  or  renculi. 
In  some  animals,  e.g.,  the  guinea- 
pig  and  rabbit,  the  entire  kidney 
consists  of  a  sirgle  lobe  (Fig. 
194.).  In  the  adult  human  kid- 
ney the  division  into  lobes  is  not 
complete,  the  peripheral  parts 
of  the  different  lobes  blending. 
Rarely  the  foetal  division  into 
lobes  persists  in  adult  life,  such 
as  kidney  being  known  as  a 
"lobulated  kidney." 

On  the  mesially  directed  side 
of  the  kidney  is  a  depression 
known  as  the  hilum  (Fig.  194). 
This  serves  as  the  point  of  en- 
trance of  the  renal  artery  and  of 
exit  for  the  renal  vein  and  ureter. 
On  section,  a  division  of  the 
organ  into  two  zones  is  apparent 
to  the  naked  eye  (Figs.  194  and 
195;.  The  outer  zone  or  cortex 
has  a  granular  appearance,  while  the  inner  zone  or  medulla  shows 
radial  striations.  This  difference  in  appearance  between  cortex  and 
medulla  is  mainly  due,  as  will  be  seen  subsequently,  to  the  fact  that 
in  the  cortex  the  kidney  tubules  are  convoluted,  while  in  the  medulla 

286 


Fig.  194. — Longitudinal  Section  Through 
Kidney  of  Guinea-pig,  including  hilum  and 
beginning  of  ureter.  X  5.  (Technic  i,  p. 
302.)  a,  Pelvis;  6,  papilla;  c,  wall  of  pelvis; 
d,  ureter;  e,  ducts  of  Bellini;  /,  cortical 
pyramids;  g,  medullary  rays;  h,  cortex; 
i,  medulla;  j,  renal  corpuscles. 


THE  URIX.^J^Y  SYSTEM. 


2S7 


they  run  in  parallel  radial  lines  alternating  witii  straight  blood-vessels. 
The  medullan-  portion  of  the  kidney  projects  into  the  pelvis,  or  upper 
expanded  beginning  of  the  ureter  (Figs.  194  and  195)  in  tlie  form  of 


Fig.  iQs. 


F:..  ioc. 


Fig.  1 05. — Longitudiriai  Section  of  Kiduer  ThroiigJa  MUlnuim.    a,  CorticaS  pviaaiaid:  h. 
medullar}-  rav;  r,  medulla;  if,  cortex;  t.  renal  ca.lj5;_/",  Mlum;  g,  Tureter;  A,  rertal  i'T- 
7,  obliquely  cut  tubules  of  medulla;  7  and  t,  renal  arches;  7,  coIuttiti  of  Benim;  w,,  cor.- , 
tissue  and  fat  surrounding  renal  vessels;  w,  medulla  cui  obliquelj;  p.  papilla;  ^,  mec—.-r- 
p}-Tamid.     (Merkel-Henle.) 

Fig.  106. — Scheme  of  Urimferotis  Tubule  aud  of  tie  Blood-Tessels  of  ibe  Kidner 
sho-w-ing  their  relation  to  eaci  otter  and  to  the  different  parts  of  the  tjdner.  <J,  GioioeT- 
ulus;  BC.  BoTvman's  capsule;  A",  neck;  PC,  proximal  conroluted  tubule;  .S,  sgsiral  Tubuie; 
D,  descending  arm  of  Henle's  loop;  L,  Henle's  loop;  .4,  ascending  arm  of  Henle's  loop; 
I, DC,  distal  convoluted  tubule;  .4C,  arched  tubule;  iSC,  straight  collerdng  rubule;  EJ?. 
duct  of  Bellini;  A,  arcuate  art  err,  and  F,  arcuate  vein,  giving  off  interlobulaT  vessels  to 
cortex  and  vasa  recta  to  medulla;  a,  afferent  vessel  of  glomerulus;  f,  efferent  vessel  off 
glomerulus;  r,  capillary  network  in  cortical  labyrinth;  .^.  stellate  veins;  tt,  vasa  recta  aasd 
capillary  network  of  medulla.     (Peajsol.) 


papiUd.  The  number  of  papillae  varies,  from  ten  to  fifteen,  correspond- 
ing to  the  number  of  lobes  in  the  foetal  kidney.  The  pyramidal  segment 
of  medulla,  the  apex  of  which  is  a  papilla — in  other  words,  the  medullaij 


288 


THE  ORGANS. 


portion  of  a  foetal  lobe — is  known  as  a  medullary  or  Malpighian  pyra- 
mid. The  extensions  downward  of  cortical  substance  between  the 
Malpighian  pyramids  constitute  the  columns  of  BertiitT^or  septa  renis. 
Radiating  lines — medullary  rays  or  pyramids  of  Ferrein — extend  out- 
ward from  the  base  of  each  Malpighian  pyramid  into  the  cortex  (Fig. 
195).  As  the  rays  extend  outward  in  groups  they  oudine  pyramidal 
cortical  areas.  These  are  known  as  the  cortical  pyramids  or  cortical 
labyrinths. 

The  secreting  portion  of  the  kidney  is  composed  of  a  large  number 
of  long  tortuous  tubules,  the  uriniferous  tubules. 

Each  URINIFEROUS  TUBULE  begins  in  an  expansion  known  as 
Bowman's  capsule  (Figs.  196,  BC,  and  197,  3,  4,  5).     This  encloses  a 


Fig.  197. — Diagrams  Illustrating  Successive  Stages  in  Development  of  the  Renal 
Corpuscle,  i  and  2,  Approach  of  blood-vessel  and  blind  end  of  tubule;  3,  invagination  of 
tubule  by  blood-vessels;  4  and  5,  later  stages,  showing  development  of  glomerulus  and  of 
the  two-layered  capsule  of  the  renal  corpuscle,  the  outer  layer  being  the  capsule  of  Bowman 
continuous  with  the  epithelium  of  the  first  convoluted  tubule. 

tuft  of  blood  capillaries,  the  glomerulus.  Bowman's  capsule  and  the 
glomerulus  together  constitute  the  Malpighian  body  or  renal  corpuscle. 
(Fig.  198).  As  it  leaves  the  Malpighian  body  the  uriniferous  tubule 
becomes  constricted  to  form  the  neck  (Figs.  196,  N,  197,  and  198  b). 
It  next  broadens  out  into  a  greatly  convoluted  portion,  i\\Q  first  con- 
voluted tubule  (Fig.  196,  PC,  and  Fig.  199).  The  Malpighian  body, 
the  neck,  and  the  first  convoluted  tubule  are  situated  in  the  cortical 
pyramid  (Fig.  196).  The  tubule  next  takes  a  quite  straight  course 
downward  into  the  medulla — descending  arm  of  HenWs  loop  (Fig.  196, 
D) — turns  sharply  upon  itself — Henle's  loop  (Fig.  196,!.) — and  passes 
again  toward  the  surface — ascending  arm  of  Henle's  loop  (Fig.  196, 
A) — through  the  medulla  and  medullary  ray.  Leaving  the  medullary 
ray,  it  enters  the  same  cortical  pyramid  from  which  it  took  origin  to 


THE  URINARY  SYSTEM.  289 

become  the  second  convoluted  tubule  (Fig.  196,  DC).  This  tubule  is  in 
close  proximity  to  the  Malpighian  body  from  which  it  started,  lying, 
however,  on  the  side  of  the  afferent  and  efferent  blood-vessels,  i.e.,  on 
the  side  opposite  its  point  of  origin.  The  second  convoluted  tubule 
passes  into  the  arched  tubule  {AC)  which  enters  a  medullary  ray  and 
continues  straight  down  through  the  medullary  ray  and  medulla  as 
the  straight  or  collecting  tubule  iSC).  During  its  course  the  collecting 
tubule  receives  other  arched  tubules.  As  it  descends  it  becomes 
broader,  enters  the  papilla,  where  it  is  known  as  the  duct  of  Bellin 
(ED),  and  opens  on  the  surface  of  the  papilla  into  the  kidney  pelvis 
About  twenty  ducts  of  Bellini  open  upon  the  surface  of  each  papilla 
their  openings  being  known  as  the  foramina  pa  pillar  ia. 


Fig.   ig8. — Malpighian  Bodv  from  Human  Kidnc-.      X  2S0.     (Technic  2,  p.  502.)     a, 
Bowman's  capsule;  h.  neck;  r,  first  convoluted  tubule;  (/,  afferent  and  efferent  vessels. 

Each  tubule  consists  of  a  delicate  homogeneous  membrana  propria 
upon  which  rests  a  single  layer  of  epithelial  cells.  The  shape  and 
structure  of  the  epithelium  differ  in  different   portions  of  the  tubule. 

I.  The  Malpighian  body  is  spheroidal,  and  has  a  diameter  of  from 
120  to  200 «.  The  structure  of  the  Malpighian  body  can  be  best 
understood  by  reference  to  its  development  (Fig.  197).  During  the 
development  of  the  uriniferous  tubules  and  of  the  blood-vessels  of  the 
kidney,  the  growing  end  of  a  vessel  meets  the  growing  end  of  a  tubule 
in  such  a  way  that  there  is  an  invagination  of  the  tubule  by  the  blood- 
\'csscl  (see  Fig.  197).  The  result  is  that  the  end  of  the  ^"essel  which 
develops  a  tuft-like  network  of  capillaries — the  glomerulus — comes  to 
lie  within  the  expanded  end  of  the  tubule,  which  thus  forms  a  two- 
layered  capsule  for  the  glomerulus.  One  layer  of  the  capsule  closely 
invests  the  tuft  of  capillaries,  dipping  down  into  it  and  separating  the 
19 


290  THE  ORGANS. 

groups  of  capillaries  (see  p.  294).  This  layer  by  modification  of  the 
original  epithelium  of  the  tubule  is  finally  composed  of  a  single  layer  of 
flat  epithelial  cells  with  projecting  nuclei.  The  outer  layer  of  the 
capsule  lies  against  the  delicate  connective  tissue  which  surrounds 
the  Malpighian  body.  This  layer  consists  of  a  similar  though  slightly 
higher  epithelium  and  is  known  as  Bowman^s  capsule.  Between  the 
glomerular  layer  of  the  capsule  and  Bowman's  capsule  proper  is  a 
space  which  represents  the  beginning  of  the  lumen  of  the  uriniferous 
tubule  (Fig.  198),  the  epithelium  of  Bowman's  capsule  being  directly 
continuous  with  that  of  the  neck  of  the  tubule. 

B 


'^^i^'' 


A 

Fig.  199. — Proximal  Convoluted  Tubules  of  Human  Kidney.      X  350.     (Technic  2,  p, 

302.)     A,  Cross-section;  B,  oblique  section. 

2.  The  Neck. — This  is  short  and  narrow,  and  is  lined  by  a  few 
cuboidal  epithelial  cells.  Toward  its  glomerular  end  the  epithelium 
is  transitional  between  the  flat  epithelium  of  Bowman's  capsule  and 
the  cuboidal  epithelium  of  the  neck  proper.  At  its  other  end  the 
epithelium  of  the  neck  becomes  larger  and  more  irregular  as  it  passes 
over  into  that  lining  the  next  division  of  the  tubule   (Fig.  198). 

3.  The  first  convoluted  tubule  (Fig.  199)  measures  from  40  to  yo/t 
in  diameter.  It  is  lined  by  irregularly  cuboidal  or  pyramidal  epithe- 
hum,  with  very  indistinct  demarcation  between  the  cells.  The  cyto- 
plasm is  granular,  and  the  granules  are  arranged  in  rows,  giving  the  cell 
a  striated  appearance.  This  is  especially  marked  at  the  basal  end  of 
the  cell  where  the  nucleus  is  situated.  A  zone  of  fine  striations  along 
the  free  surface  frequently  presents  somewhat  the  appearance  of  cilia. 

4.  The  descending  arm  of  Henle^s  loop  is  narrow  (Fig.  200,  i),  10 
to  15/y.  in  diameter.  It  is  lined  by  a  simple  flat  epithelium.  The  part 
of  the  cell  which  contains  the  nucleus  bulges  into  the  lumen,  and  as  the 


THE  URINARY  SYSTEM.  291 

nuclei  of  opposite  sides  of  the  tubule  usually  alternate,  the  lumen  is 
apt  to  present  a  wavy  appearance  in  longitudinal  sections. 

5.  Henle's  Loop. — The  epithelium  here  changes  from  the  flat  of 
the  descending  arm  to  the  cuboidal  of  the  ascending  arm.  The  exact 
point  where  the  transition  occurs  varies.  It  may  take  place  during 
the  turn  of  the  loop,  or  in  either  the  ascending  or  descending  arm. 


I 


■m.      ■ 

Ml         1 

'0, 

1 

M 

i 
1  ■  ■  ■ 

m 


'■'      |i 


s@! 


■-■ ;■  ,       '»i:-''j 

Fig.  200. — Tubules  of  Human  Kidney.  X  560.  From  longitudinal  section.  (Tech- 
nic  2,  p.  302.)  I,  Descending  arm  of  Henle's  loop;  2,  ascending  arm  of  Henle's  loop;  3, 
collecting  tubule;  4,  duct  of  Bellini.  Beneath  the  longitudinal  sections  are  seen  cross 
sections  of  the  same  tubules. 

6.  The  ascending  arm  of  Henle^s  loop  (Fig.  200,  2)  is  broader 
than  the  descending,  measuring  from  20  to  7,0/1  in  diameter.  Its 
epithelium  is  cuboidal  with  granular  striated  protoplasm.  The  cells 
thus  resemble  those  of  the  convoluted  tubule,  but  are  smaller,  more 
regular,  and  less  granular. 

7.  The  second  convoluted  tubule  has  a  diameter  of  40  to  50/^.  It  is 
much  less  tortuous  than  the  first  convoluted  tubule.  Its  epithelium  is 
similar  to  that  lining  the  first  convoluted  tubule  except  that  it  is  slightly 
lower  and  less  distinctly  striated. 

8.  The  arched  tubule  has  a  somewhat  narrower  lumen  (about  2^/1) 
than  the  second  convoluted.  It  is  lined  with  a  low  cuboidal  epithelium 
with  only  slightly  granular  cytoplasm. 

g.  The  straigJit  or  collecting  tubule  (Fig.  200,  3)  has  at  its  commence- 


292 


THE  ORGANS. 


ment  at  the  apex  of  a  medullary  ray  a  diameter  of  from  40  to  50/i 
As  it  descends  it  receives  other  arched  tubules,  and  increases  in  diameter 
until  in  the  ducts  of  Bellini  (Fig.  200,  4)  of  the  papilla  it  has  a  diameter 
of  from  200  to  300«  and  a  widely  open  lumen.  The  epithelium  is  at 
first  low  and  gradually  increases  in  height.     In  the  ducts  of  Bellini  it  is 


:">f-. 


:* 


^'^v 


Fig.  201. — Cross  Section  Through  Cortex  of  Human  Kidney.  X  60.  (Technic  2, 
p.  302.)  a,  Convoluted  tubules  of  cortical  pyramid;  h,  interlobular  artery;  f,  medullary 
rays;  d,  Malpighian  bodies. 

of  the  high  columnar  type.  The  cytoplasm  of  these  cells  contains 
comparatively  few  granules,  thus  appearing  transparent  in  contrast 
with  the  granular  cytoplasm  of  the  ascending  arms  of  Henle's  loops 
and  of  the  convoluted  tubules. 


Location  in  tiidney 


Cortical  labyrinth 


Portion  of  tubule  Epithelium 

I  Bowman's  capsule.  ,      Flat  with  bulging  nuclei. 

Neck Cuboidal  granular. 

I  First  convoluted,  .  .  .      Pyramidal,  granular;  large  cells 
I  with      granules       in       rows, 

J  ■  giving     striated     appearance; 

striated    free     border;     indis- 
tinct cell  outline. 
Second  convoluted         Similar  to   preceding,   but   cells 
not  so  distinctly  striated  and 
more  regular  in  shape. 


THE  URINARY  SYSTEM. 


293 


Location  in  kidney  Portion  of  tubule  Epithelium 

Arched  (passing  from     Rather  clear  cuboidal  cells. 

labyrinth  to  ray) 
Part  of  ascending  arm     Cuboidal,  granular,  regular. 
Medullary  ray  in  cortex .  i       Henle's  loop 

Collecting  tubule.  .  .  Cuboidal  or  columnar,  clear; 
varying  in  height  with  diam- 
eter of  tubule. 

Decendingarm,Hen-     Clear    flat    cells    with    bulging 
le's  loop  nuclei. 

Henle's  loop Usually  like  descending,   rarely 

like  ascending  arm. 
Part     of     ascending     Cuboidal,  granular. 

arm  Henle's  loop 
Collecting  tubule.  .  .      Cuboidal    or    columnar,    clear; 
varying  in  height  with  diam- 
eter of  tubule. 

Papilla Ducts  of  Bellini ....      Clear,  cuboidal  or  columnar  cells 

according     to     diameter      of 
tubule. 


Medulla . 


The  epithelium  of  the  uriniferous  tubule  rests  upon  an  apparently 
structureless  basement  membrane.  Riihle  describes  the  basement 
membrane  as  consisting  of  delicate  longitudinal  and  circular  connect- 
ive-tissue fibrils.  He  regards  the  fibrils  as  merely  a  more  regular 
arrangement  of  the  interstitial  connective  tissue.  According  to 
Riihle  the  epithelium  simply  rests  upon  the  basement  membrane,  being 
in  no  way  connected  with  it.  In  the  cortex  the  tubules  are  closely 
packed  and  the  amount  of  interstitial  connective  tissue  is  extremely 
small.     In  the  medulla  the  connective  tissue  is  more  abundant. 

Of  the  function  of  the  different  parts  of  the  uriniferous  tubule  our 
knowledge  is  extremely  limited.  The  water  of  the  urine  is  secreted 
in  the  Malpighian  body,  some  specific  action  of  the  cells  covering  the 
glomerulus,  allowing  the  water,  normally  free  from  albumen,  to  pass 
from  the  capillaries  into  the  lumen  of  the  tubule.  The  urinary  solids 
are  secreted  mainly  or  wholly  by  the  cells  of  the  convoluted  tubule 
and  of  the  ascending  arm  of  Henle's  loop. 

Blood-vessels  (diagram,  Fig.  203). — The  blood  supply  to  the 
kidney  is  rich  and  the  blood-vessels  come  into  intimate  relations  with 
the  tubules.  The  renal  artery  enters  the  kidney  at  the  hilum.  and 
immediately  splits  up  into  a  numl)er  of  branches — the  interlobar  arteries 
(Fig  203,  g).     These  give  otT  twigs  to  the  calyces  and  to  the  capsule,  then 


294  THE  ORGANS. 

without  further  branching  pass  between  the  papillae  through  the 
medulla  to  the  junction  of  medulla  and  cortex.  Here  they  bend 
sharply  at  right  angles  and  following  the  boundary  line  between  cortex 
and  medulla,  form  a  series  of  arches,  the  artericE  arciformes  or  arcuate 
arteries  (Fig.  203,  d).  From  the  arcuate  arteries  two  sets  of  vessels 
arise,  one  supplying  the  cortex,  the  other  the  medulla   (Figs.  196  and 

203). 

The  arteries  to  the  cortex  spring  from  the  outer  (Fig.  203,  h)  sides  of 
the  arterial  arches,  and  as  interlobular  arteries  pursue  a  quite  straight 


^    ^^    /0\.,    /^        ^) 


^^  / 


i^^'v 


c. 


O       -'  I    J       -^  ^ 


\j 


^yis 


Fig.  202. — Cross  Section  through  Medulla  of  Human  Kidney.  X  465.  (Technic  2, 
p.  302.)  a,  Capjillaries;  h,  collecting  tubule;  c,  ascending  arms  of  Henle's  loops;  d,  descend- 
ing arms  of  Henle's  loops. 

course  through  the  cortical  pyramids  toward  the  surface,  about  mid- 
way between  adjacent  medullary  rays.  From  each  interlobular  artery 
are  given  off  numerous  short  lateral  branches,  each  one  of  which  passes 
to  a  Malpighian  body.  Entering  a  Malpighian  body  as  its  afferent 
vessel,  the  artery  breaks  up  into  a  number  of  small  arterioles,  which 
in  turn  give  rise  to  the  groups  of  capillaries  which  form  the  glomerulus. 
Each  group  of  glomerular  capillaries  arising  from  a  single  arteriole  is 
separated  from  its  neighbors  by  a  rather  larger  amount  of  connective 


THE  URINARY  SYSTEM. 


295 


tissue  than  that  which  separates  the  individual  capillaries.  This 
gives  to  the  glomerulus  its  lobular  appearance.  From  the  smaller 
glomerular  capillaries  the  blood  passes  into  somewhat  larger  capillaries, 
which  unite  to  form  the  efferent  vessel  of  the  glomerulus.     As  afferent 


Fig.  203. — Diagram  to  Illustrate  (left)  the  Course  of  the  Uriniferous  Tubule:  (right) 
the  Course  of  the  Renal  Vessels.  (Szymonowicz.)  A,  B,  C,  D,  form  the  kidney  lohidcs; 
a,  afferent  vessel;  e,  efferent  vessel  of  glomerulus;  i,  Bowman's  capsule;  2,  first  convoluted 
tubule;  3,  descending  arm  of  Henle's  loop;  4,  ascending  arm  of  Henle's  loop;  5,  second  con- 
voluted tubule;  6  and  7,  collecting  tubules;  8,  duct  of  Bellini;  b,  interlobular  artery;  c,  inter- 
lobular vein;  d,  renal  arch  (arcuate  artery  above  and  arcuate  vein  below) ;  /,  interlobar  vein ; 
g,  interlobar  artery;  h,  medulla;  i,  medullary  ray;  7,  cortex. 


and  efferent  vessels  lie  side  by  side,  the  glomerulus  has  the  appearance 
of  being  suspended  from  this  point  (Figs.  196, 198) .  The  en/ ire  vascular 
system  of  the  glomerulus  is  arterial. 

After  leaving    the  glomerulus,  the  efferent  vessel  breaks  up  into  a 
second  system  of  capillaries,  which  form  a  dense  network  among  the 


296  THE  ORG.\NS. 

tubules  of  the  cortical  pyramids  and  of  the  medullary  rays.  The 
mesh  corresponds  to  the  shape  of  the  tubules,  being  irregular  in  the 
pyramids,  long  and  narrow  in  the  rays.  In  these  capillaries  the  blood 
gradually  becomes  venous  and  passes  into  the  interlobular  veins  (Fig. 
203,  c).  These  accompany  the  interlobular  arteries  to  the  boundary 
between  cortex  and  medulla,  where  they  enter  the  arcuate  veins,  which 
accompany  the  arcuate  arteries  (Fig.  20T,,d). 

The  main  arteries  to  the  medulla  arise  from  the  inner  concave  sides 
of  the  arterial  arches.  They  pass  straight  down  among  the  tubules 
of  the  medulla  and  are  known  as  arterice  rectce.  Branching,  they  give 
rise  to  a  long-meshed  capillary  network  which  surrounds  the  tubules. 
This  capillary  network  is  also  supplied  by  (i)  efferent  vessels  from  the 
more  deeply  situated  glomeruli  (false  arteriae  rectse)  and  (2)  by  medul- 
lary branches  from  the  interlobular  arteries.  The  veins  of  the  medulla 
arise  from  the  capillary  network  and  follow  the  arteries  back  to  the 
junction  of  medulla  and  cortex,  where  they  empty  into  the  arcuate 
veins  (Fig.  203,  d). 

In  addition  to  the  distribution  just  described,  some  of  the  inter- 
lobular arteries  extend  to  the  surface  of  the  kidney,  where  they  enter 
the  capsule  and  form  a  network  of  capillaries  which  anastomose  with 
capillaries  of  the  suprarenal,  recurrent,  and  phrenic  arteries.  A 
further  collateral  circulation  is  established  by  branches  of  the  above- 
named  arteries  penetrating  the  kidney  and  forming  capillary  networks 
within  the  cortex,  even  supplying  some  of  the  more  superficial  glomeruli. 
The  most  superficial  of  the  small  veins  which  enter  the  interlobular 
are  arranged  in  radial  groups,  having  the  interlobular  veins  as  their 
centres.  These  lie  just  beneath  the  capsule,  and  are  known  as  the 
stellate  veins  of  Verheyn.  In  addition  to  capillary  anastomoses,  direct 
communication  between  arteries  and  veins  of  both  cortex  and  medulla, 
by  means  of  trunks  of  considerable  size,  has  been  described. 

The  lymph  vessels  of  the  kidney  are  arranged  in  two  systems,  a 
superficial  system  which  ramifies  in  the  capsule,  and  a  deep  system 
which  accompanies  the  arteries  to  the  parenchyma  of  the  organ. 
Little  is  known  of  the  relation  of  the  lymphatics  to  the  kidney 
tubules. 

Nerves. — These  are  derived  from  both  cerebro-spinal  and  sym- 
pathetic systems.  The  medullated  fibres  appear  to  pass  mainly  to 
the  walls  of  the  blood-vessels  which  supply  the  kidney  capsule.  Plex- 
uses of  fine  non-medullated  fibres  (sympathetic)  accompany  the 
arteries  to  the  glomeruli.     Delicate  terminals  have  been  described  as 


THE  URINARY  SYSTEM.  297 

passing  from  these  plexuses,  piercing  the  basement  membrane  and 
ending  freely  between  the  epithelial  cells  of  the  tubules. 

The  Kidney-Pelvis  and  Ureter. 

The  kidney-pelvis,  with  its  subdi\"isions  the  calyces,  and  the  ureter 
constitute  the  main  excretory  duct  of  the  kidney.  Their  walls  consist 
of  three  coats;  an  inner  mucous,  a  middle  muscular,  and  an  outer 
fibrous. 

The  mucosa  is  lined  by  epithelium  of  the  transitional  type.  There 
are  from  four  to  eight  layers  of  cells,  the  cell  outlines  are  usually  well 
defined,  and  the  surface  cells  instead  of  being  distinctly  squamous  are 
only  slightly  flattened.  Less  commonly  large  flat  plate-like  cells,  each 
containing  several  nuclei,  are  present.  The  cells  rest  upon  a  base- 
ment membrane,  beneath  which  is  a  stroma  of  delicate  fibro-elastic 
tissue  rich  in  cells.  Difl'use  lymphatic  tissue  frequently  occurs  in  the 
stroma,  especially  of  the  pelvis.  Occasionally  the  lymphatic  tissue 
takes  the  form  of  small  nodules.  Mucous  glands  in  small  numbers 
are  found  in  the  stroma  of  the  pelvis  and  upper  part  of  the  ureter. 
There  is  no  distinct  submucosa,  although  the  outer  part  of  the  stroma 
is  sometimes  referred  to  as  such. 

The  muscularis  consists  of  an  inner  longitudinal  and  an  outer 
circular  layer.  In  the  lower  part  of  the  ureter  a  discontinuous  outer 
longitudinal  layer  is  added. 

The  fibrosa  consists  of  loosely  arranged  connective  tissue  and 
contains  many  large  blood-vessels.  It  is  not  sharply  limited  exter- 
nally, but  blends  with  the  connective  tissue  of  surrounding  structures, 
and  serves  to  attach  the  ureter  to  the  latter. 

The  larger  blood-vessels  run  in  the  fibrous  coat.  From  these, 
branches  pierce  the  muscular  layer,  give  rise  to  a  capillary  network 
among  the  muscle  cells,  and  then  pass  to  the  mucosa,  in  the  stroma 
of  which  they  break  up  into  a  rich  network  of  capillaries.  The  veins 
follow  the  arteries. 

The  lymphatics  follow  the  blood-vessels,  being  especially  numer- 
ous in  the  stroma  of  the  mucosa. 

Nerves. — Plexuses  of  both  medullated  and  non-medullated  fibres 
occur  in  the  walls  of  the  ureter  and  pelvis.  The  non-medullated 
fibres  pass  mainly  to  the  cells  of  the  muscularis.  Medullated  fibres 
enter  the  mucosa  where  they  lose  their  medullary  sheaths.  Terminals 
of  these  fibres  have  been  traced  to  the  lining  epithelium. 


298  THE  ORGANS. 

The  Urinary  Bladder. 

The  walls  of  the  bladder  are  similar  in  structure  to  those  of  the 
ureter. 

The  mucous  membrane  is  thrown  up  into  folds  or  is  comparatively 
smooth,  according  to  the  degree  of  distention  of  the  organ.  The 
epithelium  is  of  the  same  general  type — transitional  epithelium  (see 
page  67) — as  that  of  the  ureter.  The  number  of  layers  of  cells  and 
the  shapes  of  the  cells  depend  largely  upon  whether  the  bladder  is 


''M^Mi/:^ 


'<-<£ai\> 


Fig.  204. — ^Vertical  Section  through  Wall  of  moderately  distended  Human  Bladder. 
X  60.  (Technic  5,  p.  302.)  a,  Epithelium,  h,  stroma,  of  mucous  membrane;  c,  sub- 
mucosa;  d,  inner  muscle  layer;  e,  middle  muscle  layer;/,  outer  muscle  layer. 

full  or  empty.  In  the  collapsed  organ  the  superficial  cells  are  cuboidal 
or  even  columnar,  their  under  surfaces  being  marked  by  pit-like 
depressions  caused  by  pressure  of  underlying  cells.  Beneath  the 
superficial  cells  are  several  layers  of  polygonal  cells,  while  upon  the 
basement  membrane  is  the  usual  single  layer  of  small  cuboidal  cells. 
In  the  moderately  distended  bladder  the  superficial  cells  become 
flatter  and  the  entire  epithelium  thinner  (Fig.  204).  In  the  distended 
organ  there  is  still  further  flattening  of  the  superficial  cells  and  thinning 
of  the  entire  epithelium.     The  stroma  consists  of  fine  loosely  arranged 


THE  URINARY  SYSTEM.  299 

connective  tissue  containing  many  lymphoid  cells  and  sometimes  small 
lymph  nodules.  It  merges  without  distinct  demarcation  into  the  less 
cellular  suhmucosa  (Fig.  204,  c). 

The  three  muscular  layers  of  the  lower  part  of  the  ureter  are  con- 
tinued on  to  the  bladder,  where  the  muscle  bundles  of  the  different 
layers  interlace  and  anastomose,  but  can  be  still  indistinctly  differ- 
entiated into  an  inner  longitudinal,  a  middle  circular,  and  an  outer 
longitudinal  layer  (Fig.  204,  d,  e,f). 

The  fibrous  layer  is  similar  to  that  of  the  ureter,  and  attaches  the 
organ  to  the  surrounding  structures. 

The  blood-  and  l5miph-vessels  have  a  distribution  similar  to  those 
of  the  ureter. 

Nerves. — Sensory  medullated  fibres  pierce  the  muscularis,  branch 
repeatedly  in  the  stroma,  lose  their  medullary  sheaths,  and  terminate 
among  the  cells  of  the  lining  epithelium.  Sympathetic  fibres  form 
plexuses  in  the  fibrous  coat,  where  they  are  interspersed  with  numerous 
small  groups  of  ganglion  cells.  Axones  of  these  sympathetic  neurones 
penetrate  the  muscularis.  Here  they  form  plexuses,  from  which  are 
given  off  terminals  to  the  individual  muscle  cells. 

For  development  of  urinary  system  see  page  346. 

The  Suprarenal  Gland. 

The  suprarenal  is  a  ductless  gland  situated  on  the  upper  and  ante- 
rior surface  of  the  kidney.  It  is  surrounded  by  a  capsule  and  consists 
of  an  outer  zone  or  cortex  and  a  central  porton  or  medulla.  The  cortex 
and  medulla  are  sharply  differentiated  both  in  general  appearance,  and 
in  histological  structure.  The  former  is  of  rather  firm  consistency, 
its  cells  are  arranged  in  rows  with  the  blood-vessels  between  them, 
giving  the  zone  a  striated  appearance.  Its  cells  contain  fat  droplets 
and  peculiar  granules  known  as  lipoid  granules  which  give  the  cortex  a 
yellowish  tint.  In  contrast  the  medulla  is  soft,  vascular,  has  a  dark 
reddish  appearance,  and  its  cells  contain  granules  known  as  chromaffin 
or  pJiceochrome  granules. 

The  CAPSULE  (Fig.  205,  ,4)  is  composed  of  fibrous  connective  tissue 
and  smooth  muscle.  In  the  outer  part  of  the  capsule  the  connective 
tissue  is  loosely  arranged  and  merges  with  the  surrounding  fatty  areolar 
tissue.  The  inner  layer  of  the  capsule  is  more  dense  and  forms  a  firm 
investment  for  the  underlying  glandular  tissue.  From  the  capsule 
trabeculae  extend  into  the  orran  forming;  its  framework  and  outlining 


300 


THE  ORGANS. 


compartments,  which  contain  the  glandular  epithelium.     This  con- 
nective tissue  is  reticular  in  character. 

The  CORTEX  (Fig.  205,  B)  is  subdivided  into  three  layers  or  zones: 

(a)  A  narrow,  superficial  layer,  the 
glomerular  zone;  (b)  a  broad  middle 
layer,  the  fascicular  zone;  and  (c)  a 
narrow  deep  layer,  the  reticular  zone. 
The  names  of  the  layers  are  indicative 
of  the  shape  of  the  connective-tissue- 
enclosed  compartments  and  of  the 
contained  groups  of  gland  cells.  In 
the  glomerular  zone  (Fig.  205,  a)  the 
high,  irregularly  columnar  epithelium 
is  arranged  in  spherical  or  oval  groups. 
The  protoplasm  of  the  cells  is  granular, 
and  their  nuclei  are  rich  in  chromatin. 
In  the  fascicular  zone  (Fig.  205,  h) 
polyhedral  cells  are  arranged  in  long 
columns  or  fascicles.  The  cytoplasm 
is  granular  and  usually  contains  some 
or  many  fat  droplets.  The  nuclei 
contain  less  chromatin  than  those  in 
the  glomerular  zone.  In  the  reticular 
zone  (Fig.  205,  c)  similar  though  some- 
what more  darkly  staining  cells  form 
a  coarse  reticulum  of  irregular  anas- 
tomosing cords. 

The  MEDULLA  (Fig.  205,  C)  con- 
sists of  spherical  and  oval  groups  and 
cords  of  polygonal  cells.  After  alcohol 
or  formalin  fixation  these  cells  take  a 

renal."  (Merkcl-Henle.)    .4 ,  cl'psule ;     P^l^^   ^tain    than    those   of   the  COrtCX. 

5,  cortex;  C,  medulla;  a,  glomerular    After  fixation  in  solutions  Containing 

zone;  b,  fascicular  zone;  c,  reticular  ... 

zone;  v,  vein  in  medulla.  chromic  acid  or  chrome  salts  the  cells 

of  the  medulla  assume  a  peculiar 
characteristic  deep  brown  color,  which  cannot  be  removed  by  washing 
in  water  and  which  is  due  to  chromaffin  granules  which  they  contain. 
Scattered  in  irregular  groups  among  these  cells  are  many  sympathetic 
ganglion  cells. 

Blood-vessels. — The  arteries  supplying  the  suprarenal  first  form  a 


THE  URINARY  SYSTEM.  3U1 

poorly  defined  plexus  in  the  capsule.  From  this  are  given  off  three 
sets  of  vessels — one  to  the  capsule,  one  to  the  cortex,  and  one  to  the 
medulla.  The  first  set  breaks  up  into  a  network  of  capillaries,  which 
supply  the  capsule.  The  vessels  to  the  cortex  break  up  into  capillary 
networks,  the  shape  of  the  mesh  corresponding  to  the  arrangement  of 
the  connective  tissue  in  the  different  zones.  The  vessels  to  the  medulla 
pass  directly  through  the  cortex  without  branching  and  form  dense 
capillary  networks  among  the  groups  of  medullary  cells.  The  relations 
of  the  capillaries  to  these  gland  cells  are  extremely  intimate,  especially 
in  the  reticular  zone  and  medulla,  where  the  cells  in  many  cases  im- 
mediately surround  the  capillaries  in  much  the  same  manner  as  the 
glandular  cells  of  a  tubular  gland  surround  their  lumina.  From  the 
capillaries  of  both  cortex  and  medulla  small  veins  arise.  These  unite 
to  form  larger  veins  which  empty  into  one  or  two  main  veins  situated 
in  the  centre  of  the  medulla. 

Lymphatics. — These  follow  in  general  the  course  of  the  blood- 
vessels. The  exact  distribution  of  the  suprarenal  lymph  system  has  not 
been  as  yet  satisfactorily  determined. 

Nerves. — The  nerve  supply  of  the  suprarenal  is  so  rich  and  the 
nerve  elements  of  the  gland  are  so  abundant  as  to  have  led  to  its 
classification  by  some  among  the  organs  of  the  nervous  system.  Both 
medullated  and  non-medullated  fibres — but  chiefly  the  latter — form 
plexuses  in  the  capsule,  where  they  are  associated  with  groups  of 
sympathetic  ganglion  cells.  From  the  capsular  plexuses  fine  fibres 
pass  into  the  cortex,  where  they  form  networks  around  the  groups  of 
cortical  cells.  The  nerve  terminals  of  the  cortex  apparently  do  not 
penetrate  the  groups  of  cells.  Bundles  of  nerve  fibres,  larger  and 
more  numerous  than  those  to  the  cortex,  pass  through  the  cortex  to  the 
medulla.  Here  they  form  unusually  dense  plexuses  of  fibres,  which  not 
only  surround  the  groups  of  cells,  but  penetrate  the  groups  and  sur- 
round the  individual  cells.  iVssociated  with  the  plexuses  of  the 
medulla,  less  commonly  of  the  cortex,  are  numerous  conspicuous 
groups  of  sympathetic  ganglion  cells. 

Development. — The  cortex  and  medulla  have  entirely  dift'erent 
developmental  histories.  In  the  lower  vertebrates  (fishes)  the  two 
parts  of  the  gland  continue  separate  throughout  life.  In  the  ascending 
mammalian  scale,  the  two  parts  become  more  and  more  closely  united 
until  in  mammals  they  form  a  single  organ.  The  cortex  develops  from 
mesoderm,  first  appearing  in  embryos  of  about  five  to  six  mm.  At 
about  the  level  of  the  cephalic  third  of  the  mesonephros  the  mesothelium 


302  THE  ORGANS. 

sends  outgrowths  into  the  mesenchyme.  These  outgrowths  soon 
lose  their  connection  with  the  main  mass  of  mesothehum  and  constitute 
the  anlage  of  the  suprarenal  cortex.  The  medulla  has  an  entirely 
independent  origin,  being  derived  from  ectoderm,  as  part  of  the 
peripheral  sympathetic  nervous  system.  The  cells  of  some  of  the 
sympathetic  ganglia  differentiate  into  sympathoblasts  and  phaochromo- 
blasts,  which  give  rise  to  the  sympathetic  cells  and  chromaffin  cells 
respectively.  These  cells  soon  separate  from  their  ganglia  of  origin 
and  come  to  lie  first  near,  then  within,  the  developing  cortex,  thus 
forming  the  medulla. 

TECHNIC. 

(i)  Fix  the  simple  kidney  of  a  rabbit  or  guinea-pig  in  formalin-Miiller's  fluid 
(technic  5,  p.  7).  Make  sections  through  the  entire  organ  including  the  papilla 
and  pelvis,  stain  with  haematoxylin-eosin  (technic  i,  p.  18),  and  mount  in  balsam. 
This  section  is  for  the  study  of  the  general  topography  of  the  kidney. 

(2)  Fix  small  pieces  from  the  different  parts  of  a  human  kidney  in  formalin- 
Miiller's  fluid  or  in  Zenker's  fluid.  Thin  sections  should  be  made,  some  cutting 
the  tubules  longitudinally,  others  transversely,  stained  with  haematoxylin-eosin  and 
mounted  in  balsam. 

(3)  Blood-vessels. — For  the  purpose  of  demonstrating  blood  vessels  of  the 
kidney  the  method  of  double  injection  is  useful  (page  24). 

(4)  Ureter. — Cut  transversely  into  short  segments,  fix  in  formalin-Miiller's 
fluid  (technic  5,  p.  yj,  and  stain  transverse  sections  with  hsematoxylin-eosin  (tech- 
nic I,  p.  18),  or  with  haematoxylin-picro-acid-fuchsin  (technic  3,  p.  19).  Mount  in 
balsam. 

(5)  Bladder  (technic  i,  p.  223,  or  technic  2,  p.  223).  By  the  latter  method  any 
•desired  degree  of  distention  may  be  obtained. 

(6)  Suprarenal.  Technic  same  as  (2)  above.  Thin  vertical  sections  should 
include  both  cortex  and  medulla. 

General  References  for  Further  Study. 

Kolliker:  Handbuch  der  Gewebelehre,  vol.  iii. 

Gegenbauer:  Lehrbuch  der  Anatomie  des  Menschen,  vol.  ii. 

Henle:  Handbuch  der  Anatomie  des  Menschen,  vol.  ii. 

Johnston:  A  Reconstruction  of  a  Glomerulus  of  the  Human  Kidney.  Johns 
Hopkins  Hosp.  Bui.,  vol.  xi.,  1900. 

Miiller:   Ucber  die  Ausscheidung  des  Methylenblau  durch  die  Nieren. 
Deut.sches  Archiv  f.  klin.  Med.,  Bd.  63,  1899. 

Flint:  The  Blood-vessels,  Angiogenesis,  Organogenesis,  Reticulum  and 
Histology  of  the  Adrenal.  Contributions  to  the  Science  of  Medicine,  John  Hopkins 
Pre.ss,  1900. 

Pfaundler:  Zur  Anatomie  der  Nebenniere.     Anzeiger  Akad.  Wien,  29,  1892. 

Nagel:  Ueber  die  P^ntwickelung  des  Urogenitalsystem  des  Menschen.  Arch, 
f.  Mik.  Anat.,  Bd.  xxxiv. 


CHAPTER  IX. 

THE  REPRODUCTIVE  SYSTEM. 

I.  MALE  ORGANS. 

The  Testis. 


The  testes  are  compound  tubular  glands.  Each  testis  is  enclosed 
in  a  dense  connective-tissue  capsule,  the  tunica  albuginea  (Fig.  206,  a). 
Outside  the  latter  is  a  closed  serous  sac,  the  tunica  vaginalis,  the 
visceral  layer  of  which  is  attached  to 
the  tunica  albuginea,  while  the  parietal 
layer  lines  the  inner  surface  of  the 
scrotum.  Posteriorly  the  serous  sac  is 
wanting,  the  testis  lying  behind  and 
outside  of  the  tunica  vaginalis.  As  the 
latter  is  derived  from  the  peritoneum, 
being  brought  down  with  and  invagi- 
nated  by  the  testes  in  their  descent  to 
the  scrotum,  it  is  lined  by  mesothelial 
cells.  To  the  inner  side  of  the  tunica 
albuginea  is  a  layer  of  loose  connective 
tissue  rich  in  blood-vessels,  the  tunica 
vasculosa.  Posteriorly  the  tunica  albu- 
ginea is  greatly  thickened  to  form  the 
corpus  Highmori,  or  mediastinum  testis, 
from  which  strong  connective-tissue 
septa  radiate  (Figs.  206,  w  and  207,  b). 
These  septa  pass  completely  through 
the  organ  and  blend  with  the  tunica 
albuginea  at  various  points.  In  this 
way  the  interior  of  the  testis  is  subdi- 
vided   into    a    number    of    pyramidal 

chambers  or  lobules,  with  bases  directed  toward  the  periphery  and 
apices  at  the  mediastinum  (Figs.  206  and  207). 

Behind  the  testis  and  outside  of  its  tunica  albuginea  is  an  elongated 
body — the  epididymis  (Figs.  206,  c  and  207,  c).  consisting  of  con\"olutcd 

303 


Fig.  206. — Diagram  illustrating  the 
Course  and  Relations  of  the  Seminif- 
erous Tubules  and  their  E.xcretory 
Ducts.  (Piersol.)  a.  Tunica  albu- 
ginea; b,  connective-tissue  septum 
between  lobules;  in,  mediastinum;  /, 
convoluted  portion  of  seminiferous 
tubule;  s,  straight  tubule;  r,  rate 
testis;  e,  vasa  efferentia;  c,  tubules 
of  head  of  epididymis;  te,  vas  epi- 
didymis; vd,  vas  deferens;  va,  vas 
aberrans;  p,  paradidymis. 


304 


THE  ORGANS. 


'•??/ 


1' 


tubules  continuous  with  those  of  the  mediastinum.  The  epididymis  is 
di\ided  into  three  parts:  an  expanded  upper  extremity,  the  head  or 
globus  major  (Figs.  206  and  207,  c);  a  middle  piece,  the  body  (Fig.  207, 
(/);  and  a  shghtly  expanded  lower  extremity,  the  tail  or  globus  minor. 
From  the  last  named  passes  off  the  main  excretory  duct  of  the  testis, 
the  vas  deferens  (Fig.  206,  vd).     All  of  the  tubules  of  the  epididymis 

are  continuous  on  the  one 
hand  with  the  tubules  of 
the  testicle,  and  on  the  other 
with  the  vas  deferens. 
They  thus  constitute  a 
portion  of  the  complex  sys- 
tem of  excretory  ducts  of 
the  testicle. 

The  seminiferous 
tubule  may  be  divided 
with  reference  to  structure 
and  location  into  three 
parts,  (i)  A  much  convo- 
luted part,  the  convoluted 
tubule,  which  begins  at  the 
base  and  occupies  the 
greater  portion  of  a  lobule 
of  the  testis  (Fig.  210,  a). 
As  they  approach  the  apex 
of  a  lobule  several  of  these 
convoluted  tubules  unite  to 
form  (2)  the  straight  tubule 
(Fig.  206,  s,  210).  This 
passes  through  the  apex  of 
the  lobule  to  the  mediastinum,  where  it  unites  with  other  straight 
tubules  to  form  (3)  the  irregular  network  of  tubules  of  the  medias- 
tinum, the  rete  testis  (Fig.  210,  c). 

I.  The  Convoluted  Tubule. — This,  which  may  be  considered 
the  most  important  secreting  portion  of  the  lobule,  since  it  is  here 
that  the  spermatozoa  are  formed,  has  a  diameter  of  from  150  to  250/L 
The  tubules  begin,  some  blindly,  others  by  anastomoses  with  neigh- 
boring tubules,  near  the  periphery  of  the  lobule,  and  pursue  a  tortuous 
course  toward  its  apex  (Fig.  210,  a). 

The  wall  of  the  convoluted  tubule   (Fig.   208)   consists  of  three 


1 


Fig.  207. — Longitudinal  Secti<m  ihrougli  Human 
Testis  and  Epididymis.  X  2.  (Bohm  and  von 
Davidoff.)  The  light  strands  are  connective- 
tissue  septa,  a,  Tunica  albuginea;  b,  mediastinum 
and  rete  testis;  c,  head  of  epididymis;  d,  body  of 
epididymis;  e,  lobule;  s,  straight  tubules;  t,  vas 
epididymis. 


THE  REPRODUCTIVE  SYSTEM. 


305 


layers:  (a)  An  outer  layer  composed  of  several  rows  of  flattened  con- 
nective-tissue cells  which  closely  invest  the  tubule;  (b)  a  thin  basement 
membrane;  and  (c)  a  lining  epithelium.  The  epithelium  consists  of 
two  kinds  of  cells,  the  so-called  supporting  or  sustentacular  cells  and  the 
glandular  cells  proper,  the  spermatogenic  cells. 

The  sustentacular  cells,  or  columns  of  Sertoli,  are  irregular,  high, 
epithelial  structures,  whose  bases  rest  upon  the  basement  membrane, 


Fig.  208. — Cross  Section  of  Convoluted  Portion  of  Human  Seminiferous  Tubule. 
X  480.  (Kolliker.)  3/,  Basement  membrane;  i,  its  inner  homogeneous  layer,/?,  its  outer 
fibrous  layer;  s,  nucleus  of  Sertoli  cell;  sp,  spermatogone;  sc,  spermatocyte;  sc',  sperma- 
tocyte showing  mitosis;  sf,  nearly  mature  spermatozoon;  sf,  spermatozoon  free  in  lumen 
of  tubule;  d,  degenerating  nucleus  in  lumen;  /,  fat  droplets  stained  by  osmic  acid. 


and  which  extend  through  or  nearly  through  the  entire  epithelium 
(Fig.  209,  s).  Their  sides  show  marked  irregularities  and  depressions, 
due  to  the  pressure  of  surrounding  spermatogenic  cells.  Their  nuclei 
are  clear,  being  poor  in  chromatin  and  their  protoplasm  contains 
brownish  fat  droplets.  The  cells  of  Sertoli  have  long  been  considered 
as  sustentacular  in  character.  It  has  recently  been  suggested  that 
these  cells  are  derived  from  the  spermatogenic  cells,  but  that,  instead 
of  developing  into  spermatozoa,  they  undergo  retrograde  changes,  their 


306  THE  ORGANS. 

protoplasm  mingling  with  the  intercellular  substance,  their  nuclei 
becoming  lost  and  the  cells  finally  disappearing.  According  to  this 
theory  the  tuft-like  arrangement  of  the  spermatozoa  about  the  ends 
of  the  Sertoli  cells  is  due  to  pressure  by  surrounding  spermatogenic 
cells  (Figs.  209,  h  and  211,  /). 

h  s  b  h  f 

1 


■^^]s^ 


^N' 


?^Vv  ■  "■^.■:'  •-^^':"-->Jfe 


\~''X' 


'^.flV^f^V'^-    i,;lJ^- 


m 


.<^  l<i.\i 


St 


'■.IT 


Fig.  2og. — Parts  of  Transverse  Section  of  three  Seminiferous  Tubules  from  Testis  of 
White  Mouse.  X  600.  (Szymonowicz.)  s,  Sertoli  cell  with  nucleus;  sp,  spermatogone, 
resting  state;  sp',  spjermatogone  in  mitosis;  sc,  spermatocyte;  st,  spermatid;  sf,  spermatid  de- 
veloping into  spermatozoon;  h,  head  of  spermatozoon;  t,  tails  of  developing  spermatozoa; 
b,  blood-vessel;  c,  interstitial  cell;  m,  basal  membrane;/,  fat  droplets. 

The  appearance  which  the  spermatogenic  cells  present  depends 
upon  the  functional  condition  of  the  tubule.  In  the  resting  state  the 
epithelium  consists  of  several  layers  of  spherical  cells  containing 
nuclei  which  stain  with  varying  degrees  of  intensity.  In  the  active 
state  several  distinct  layers  of  spermatogenic  cells  can  be  differentiated. 
These  from  without  inward  are  as  follows: 

(i)  Spcrmalogones  (Figs.  208  and  2og,  sp). — These  are  small 
cuboidal  cells  which  lie  against  the  basement  membrane.  7'heir  nuclei 
are  spherical  and  rich  in  chromatin.  By  mitotic  division  of  the  sperma- 
togones are  formed  the  cells  of  the  second  layer,  the  spermatocytes. 


THE  REPRODUCTIVE  SYSTEM. 


307 


(2)  Spermatocytes  (Figs.  208  and  209.  ^r).— These  are  larger 
spherical  cells  with  abundant  cytoplasm  and  large  vesicular  nuclei 
showing  various  stages  of  mitosis.  They  form  from  two  to  four  layers 
to  the  inner  side  of  the  spermatogones,  and  -^ 

are  sometimes  differentiated  into  sperma-         ^  \ 

tocytes  of  the  first  order  and  spermatocytes  ^~~^-.^    \ 

of  the  second  order.     By  mitotic  division  N      v 

of  the  innermost  spermatocytes  are  formed  .      -V    ^ 

the  spermatids. 

(3)  The  A-/'cr;;?a//(/6' (Figs.  208  and209,5/)  \  , 
are  small  round  cells  which  line  the  lumen  -  > 


Fig.  210. 

Fig.  210. — Passage  of  Convoluted  Part  of  Seminiferous  Ti  bules  into  Stra'ght  Tubules 
and  of  these  into  the  Rete  Testis  (Milhall-iowicz.)  a,  Convoluted  part  of  tubule;  b,  fibrous 
stroma  continued  from  the  mediastinum  testis;  r,  rete  testis. 

Fig.  211. — Spermatoblast  with  some  Adjacent  Sperm  Cells,  from  Testis  of  Sparrow. 
(From  Kolliker,  after  Etzold.)  ^1/,  Basement  membrane;  s,  nucleus  of  Sertoli  cell;  sp. 
spermatogones;  sc,  spermatocyte;  st^  and  st.2,  spermatids  lying  along  the  surface  of  the 
Sertoli  cell,  s'  and  5^3;  at  st^  are  seen  the  nearly  mature  spermatozoa;  /,  tuft-like  arrange- 
ment of  bodies  of  spermatids  around  free  end  of  Sertoli  cell,  with  two  mature  spermatozoa. 

of  the  seminiferous  tubule.     They  are  the  direct  progenitors  of  the 
spermatozoa.     (For  details  of  spermatogenesis  see  page  314.) 

In  the  actively  secreting  testicle  spermatozoa  are  frequently  found 
either  free  in  the  lumen  of  the  tu!)ulc  or  with  their  heads  among  the 
superficial  cells  and  their  tails  extending  out  into  the  lumen  (Figs. 
208,  sP  and  211).     There  are  also  found  in  the  lumen  many  small 


308  THE  ORGANS. 

cells  with  dark  nuclei.     These  are  spermatids  which  have  become  free 
and  which  degenerate  without  forming  spermatozoa. 

Separating  and  supporting  the  convoluted  tubules  is  a  small 
amount  of  interstitial  connective  tissue  in  which  are  the  blood-vessels 
and  nerves.     Among  the  usual  connective-tissue  elements  are  found 

4  '/ 

x/       *      -  /,- 

i-  //^ 

"  s  J 


<«>--«rt 


c 


2^^ 


VC 


V 


,  rf»urf**»w 


-r->       ^  \      \    -    ; ' 


r 


s     r 


t 


^  '    \> 


x.-^' 


•^ 


^-»^" 

..--r-^ 


/' 


.'l'  >'    '' 


Fig.  212. — From  Section  through  Human  Mediastinum  and  Rete  Testis.  X  96. 
(Kolliker.)  A,  Artery;  F,  vein;Z,  lymph  space;  C,  canals  of  rete  testis;  5,  cords  of  tissue 
projecting  into  the  lumina  of  the  tubules  and  so  cut  transversely  or  obliquely; 5^,  section  of 
convoluted  portion  of  seminiferous  tubule. 

groups  of  rather  large  spherical  cells  with  large  nuclei — interstitial 
cells.  They  are  believed  to  represent  remains  of  the  Wolffian  body 
(Fig.  209,  c). 

2.  TuK  Straight  Tubule. — With  the  termination  of  the  con- 
voluted portion,  the  spcrmatogenic  tissue  of  the  gland  ends,  the 
remainder  of  the  tubule  constituting  a  complex  system  of  excretory 
ducts.     The  straight  tubule  is  much  narrower  than  the  convoluted, 


THE  REPRODUCTIVE  SYSTEM. 


309 


having  a  diameter  of  from  20  to  40/'..     It  is  lined  by  a  single  layer  of 
cuboidal  cells  resting  upon  a  thin  basement  membrane.     At  the  apex 
of  the  lobule  the  straight  tubules 
become  continuous  with  the  tu-  ■^ 

bules  of  the  rete  testis. 

3.  The  Tubules  of  the 
Rete  Testis. — These  are  irreg- 
ular canals  which  vary  greatly 
in  shape  and  size.  They  are 
lined  with  a  single  layer  of  low 
cuboidal  or  flat  epithelial  cells 
(Fig.  212,  C). 

The  Seminal  Ducts. — 
While    the    already    described 

straight  tubules  and  the  tubules  of  the  rete  testis  must  be  regarded 
as  part  of  the  complex  excretory  duct  system  of  the  testis,  there  are 
certain  structures  which  are  wholly  outside  the  testis  proper,  which 
serve  to  transmit  the  secretion  of  the  testis,  and  are  known  as  the  seminal 


Fig 


. — Part  of  a  Cross  Section  through  a 
\"as  Eflterens  of  the  Human  Epididymis. 
X  140.  (Kolliicer.)  F,  High  columnar 
ciliated  epithelium;  d,  lower  non-ciliated 
epithelium,  presenting  appearance  of  a 
gland;  d',  the  same  cut  obliquely. 


Fig.  214. — From  Cross  Section  through  Head  of  Ejiididymis.  X  35.  (KoUiker.) 
b.  Interstitial  connective  tissue;  c,  sections  through  tubules  of  epididvmis,  showing  two- 
layered  columnar  epithelium;  g,  blood-vessel. 

ducts.  On  lea^■ing  the  testis  these  ducts  form  the  epididymis,  after 
which  they  converge  to  form  the  main  excretorv  duct  of  the  testis,  the 
vas  deferens. 

The  Epididymis. — From  the  tubules  of  the  rete  testis  arise  from 
eight  to  lifteen  tubules,  the  vasa  efferent ia.  or  efferent  ducts  of  the 


310  THE  ORGANS. 

testis  (Fig.  206,  e).  Each  vas  efferens  pursues  a  tortuous  course,  is 
separated  from  its  fellows  by  connective  tissue,  and  forms  one  of  the 
lobules  of  the  head  of  the  epididymis.  The  epithelium  of  the  vasa 
efferentia  consists  of  two  kinds  of  cells,  high  columnar  ciliated  cells 
(Fig.  213,  F),  and,  interspersed  among  these,  low  cuboidal  non-ciliated 
cells  (Fig.  213,  d).  Occasionally  som^e  of  the  high  cells  are  free  from 
cilia  and  some  of  the  cuboidal  cells  may  bear  cilia.     The  cuboidal  cells 

lie  in  groups  between  groups  of  the 
?  ' .       ,  ,,  .  higher  cells,  often  giving  the  ap- 

'       '^  pearance  of  crypt-like  depressions. 

""  "■  "        -       ,  ,  -  •  '  These  have  been  referred  to  as  in- 

traepithelial glands.  They  do  not, 
however,  invaginate  the  underly- 
ing tissues.  The  epithelium  rests 
upon  a  basement  membrane,  be- 
neath which  are  several  layers  of 
circularly  disposed  smooth  muscle 
cells. 
T^,^  ,•   .•    1  c    .•      .V,       u  v^r  n    (         The  vasa  effcrcntia  convcrgc  to 

riG.   215. — Vertical  Section  through  Wall  of  o 

"<i<jrubule  of  Epididymis.     X  700.    (Kolli-  ioTui  the  vas  epididymis  (Fig.  214). 

/ker.)    (Fig.  214  more  highly  magnified.)     h,    tt  1      ""    •  i     i-      '    •       >    1 

Connective-tissue  and  smooth  muscle  cells;    Here  the  epithelium  IS  of  the  Stratl- 

e,  basal  layer  of  epithelial  cells; /high  col-  fig^  variety,  there    being   two  or 

umnar  epithelial  cells;  p,  pigment  granules  _ 

in  columnar  cells;  c,  cuticula;  h,  cilia.  three  rOWS  of    Cclls.       The  SUrface 

cells  are  narrow,  high,  and  ciliated, 
and  their  nuclei  are  placed  at  different  levels  (Fig.  215).  The  cilia 
are  long  and  each  cell  has  only  a  few  cilia.  The  deeper  cells  are 
irregular  in  shape.  The  basement  membrane  and  muscular  layers 
arc  the  same  as  in  the  vasa  efferentia.  As  the  vas  deferens  is  ap- 
proached the  muscular  coat  becomes  thickened,  and  is  sometimes 
strengthened  by  the  addition  of  scattered  bundles  of  longitudinally 
disposed  cells. 

Thk  Vas  Deferens. — The  walls  of  the  vas  deferens  consist  of 
four  coats — mucosa,  submucosa,  muscularis,  and  fibrosa  (Fig.  216). 

The  mucosa  is  folded  longitudinally,  and  is  composed  of  a  stroma 
and  a  lining  ejjithelium.  The  epithehum  is  of  the  stratified  columnar 
type  with  two  or  three  rows  of  cells,  being  similar  to  that  lining  the 
vas  epididymis.  The  extent  to  which  the  epithehum  is  ciliated  varies 
greatly.  In  some  cases  the  entire  vas  is  ciliated,  in  others  only  the 
upper  portion,  in  still  others  no  cilia  are  present  beyond  the  epididymis. 
The  epithelium  rests  upon  a  basement  membrane  beneath  which  is  a 


THE  REPRODUCTIVE  SYSTEM.  311 

fibro-elastic   cellular   stroma.     The   stroma   merges   without   distinct 
demarcation  into  the  more  vascular  suhmucosa. 

The  muscularis  consists  of  two  strongly  developed  layers  of  smooth 
muscle,  an  inner  circular  and  an  outer  longitudinal  (Fig.  216),  which 
together  constitute  about  seven-eighths  of  the  wall  of  the  vas.  At 
the  beginning  of  the  vas  deferens  a  third  layer  of  muscle  is  added 


^' 


--  c 
--  d 


--  ^"^^ 


Fig.  216. — Cross  Section  of  Human  Vas  Deferens.  X  37.  (Szymonowicz.)  a. 
Epithelium;  b,  stroma;  c,  submucosa;  d,  inner  circular  muscle  layer;  p,  outer  longitudinal 
muscle  layer;/,  fibrous  layer;  g,  blood-vessels. 

composed  of  longitudinal  bundles,  and  situated  between  the  inner 
circular  layer  and  the  submucosa. 

T\it  jihrosa  consists  of  fibrous  tissue  containing  many  elastic  fibres. 

Near  its  termination  the  vas  dilates  to  form  the  ampulla,  the  walls 
of  which  present  essentially  the  same  structure  as  those  of  the  ^"as. 
The  lining  c])ithelium  is,  howe^■er,  frequently  markedly  pigmented  and 
the  mucosa  contains  l)ranched  tulnilar  glands. 

The  Seminal  Vesicles  and  Ejaculatory  Ducts. — The  seminal 
vesicles.  The  walls  of  the  seminal  vesicles  are  similar  in  structure  to 
those  of  the  ampulla.  The  ei)ithclium  is  ])seudo-stratilicd  with  two 
or  three  rows  of  nuclei  and  contains  a  yellow  pigment.  When  the 
vesicles  are  distended  the  epithelium  flattens  out  and  the  nuclei  lie 
more  in  one  plane,  thus  giNing  the  ap])earance  of  an  ordinarv  simple 
columnar  epitheliimi.      Beneath  the  eiMthclitu-n  is  a  ihin  stroma,  out- 


312  THE  ORGANS. 

side  of  which  is  an  inner  circular  and  an  outer  longitudinal  layer  of 
smooth  muscle,  both  layers  being  much  less  developed  than  in  the 
vas.  The  seminal  vesicles  are  to  be  regarded  as  accessory  genital 
glands. 

The  ejaciilatovy  ducts  are  lined  with  a  single  layer  of  columnar  cells. 
The  muscularis  is  the  same  as  in  the  ampulla  except  that  the  inner 
circular  layer  is  thinner.  In  the  prostatic  portion  of  the  duct  the 
muscularis  is  indistinct,  merging  with  the  muscle  tissue  of  the  gland. 
The  ducts  empty  either  directly  into  the  urethra  or  into  the  urethra 
through  the  vesicula  prostatica. 

Rudimentary  Structures  Connected  with  the  Development  of 
the  Genital  System. — Connected  with  the  testicle  and  its  ducts  are 
remains  of  certain  foetal  structures.     These  are: 

(i)  The  paradidymis,  or  organ  of  Gir aides,  situated  between  the 
vessels  of  the  spermatic  cord  near  the  testis.  It  consists  of  several 
blind  tubules  lined  with  simple  columnar  ciliated  epithelium. 

(2)  The  ductus  aberrans  Halleri,  found  in  the  epididymis.  It  is 
lined  with  simple  columnar  ciliated  epithelium  and  opens  into  the  vas 
epididymis.  Instead  of  a  single  ductus  aberrans,  several  ducts  may 
be  present. 

(3)  The  appendix  testis  (stalked  hydatid  or  hydatid  of  Morgagni)| 
in  the  upper  part  of  the  globus  major.     It  consists  of  a  vascular  con 
nective  tissue  surrounding  a  cavity  lined  with  simple  columnar  ciliate 
epithelium: 

(4)  The  appendix  epididymidis,  a  vascular  structure,  not  always 
present,  lying  near  the  appendix  testis.  It  resembles  the  latter  in 
structure. 

The  paradidymis  and  ductus  aberrans  Halleri  probably  represent 
remains  of  the  embryonal  mesonephros.     The  appendix  testis  and  the 
appendix  epididymidis  are  believed  by  some  to  be  derived  from  the  j 
primitive  kidney,  by  others  from  the  embryonal  duct  of  Muller. 

Blood-vessels. — Branches  of  the  spermatic  artery  ramify  in  the 
mediastinum  and  in  the  tunica  vasculosa.  These  send  branches  into 
the  septa  of  the  testicle,  which  give  rise  to  a  capillary  network  among 
the  convoluted  tubules.  From  the  ca|jillaries  arise  veins  which 
accompany  the  arteries. 

Lymph  capillaries  begin  as  clefts  in  the  tunica  albuginea  and  in 
the  connective  tissue  surrounding  the  seminiferous  tubules.  These 
connect  with  the  more  dermile  lymph  vessels  of  the  mediastinum  and 
of  the  spermatic  cord. 


THE  REPRODUCTIVE  SYSTEM. 


313 


Nerves. — Non-meduUated  nerve  fibres  form  plexuses  around  the 
blood-vessels.  From  these,  fibres  pass  to  plexuses  among  the  semi- 
niferous tubules.  Their  exact 
method  of  termination  in  connec- 
tion with  the  epithelium  has  not 
been  determined.     In  the  epididy- 


Acrosome 


Head< 


Neck 


Body  ^ 


End  ring ' 


■•  Galea 
capitis 


Main  segment    ^ 
of  tail 


Anterior  end  knob 
Posterior  end  knob 


Spiral  fibers 


.Sheath  of 
axial  thread 


mis  are  found  small  sympathetic 
ganglia.  The  walls  of  the  vasa 
efferentia,  vas  epididymis,  and  vas 
deferens  contain  plexuses  of  non- 
medullated  nerve  fibres,  which  give 
oft"  terminals  to  the  smooth  muscle 
cells  and  to  the  mucosa. 

The  Spermatozoa. — The 
spermatozoa  are  the  specific  secre- 
tion of  the  testicle.  Human  sperm- 
atozoa are  long,  slender  flagellate 
bodies,  from  50  to  ~]oa  in  length, 
and  are  suspended  in  the  semen, 
which  is  a  secretion  of  the  acces- 
sory sexual  glands.  The  general 
shape  is  that  of  a  tadpole;  and  by 
means  of  an  undulatory  motion  of 
the  tail,  the  spermatozoon  is  capa- 
ble of  swimming  about  freely  in  a 
suitable  medium.  It  has  been  esti- 
mated that  the  human  spermatozoa 
average  about  sixty  thousand  per 
cubic  millimetre  of  semen. 

The  human  spermatozoon  con- 
sists of  (i)  a  head,  (2)  a  middle 
piece  or  body,  and  (3)  a  tail  or 
flagellum  (Fig.  217). 

The  head,  from  3  to  ^ix  long  and 
about  half  that  in  breadth,  is  oval 
in  shape  when  seen  on  flat,  pear- 
shaped  when  seen  on  edge.  It  con- 
sists mainly  of  chromatin  derived  from  the  nucleus  of  the  parent  cell. 
Enveloping  the  nuclear  material  of  the  head  is  a  thin  layer  or  delicate 
membrane  of  cytoplasm,   the  galea  eapitis.     The  front  of  the  head 


Axial  thread 
-Capsule 


Fig.  217. — Diagram  of  a  Human  Sperma- 
tozoon.    (Meves,  Bonnet.) 


314  THE  ORGANS. 

ends  in  a  sharp  edge,  the  apical  body  or  acrosome.  In  some  lower  forms 
the  acrosome  is  much  more  highly  developed  than  in  man  and  extends 
forward  as  a  pointed  or  barbed  spear,  the  perforatorium.  The  acro- 
some is  differentiated  from  the  nuclear  portion  of  the  head  by  taking 
an  acid  dye,  the  chromatin,  of  course,  taking  a  basic  stain. 

The  body  is  cylindrical,  about  the  same  length  as  the  head,  and 
consists  of  a  fibrillated  central  core,  the  axial  thread,  surrounded  by 
a  protoplasmic  capsule.  A  short  clear  portion,  the  neck,  unites  the 
head  and  body.  Just  behind  the  head  the  axial  thread  presents  a 
bulbous  thickening,  the  anterior  end  knob,  which  tits  into  a  depression 
in  the  head.  At  the  junction  of  neck  and  body  are  one  or  several 
posterior  end  knobs  to  which  the  axial  thread  is  attached.  The  latter 
leaves  the  body  through  a  perforated  ring,  the  end  ring  or  end  disk. 
Delicate  fibrils — spiral  fibres — run  spirally  around  the  body  portion  of 
the  axial  thread. 

The  tail  consists  of  a  main  segment,  from  40  to  6o/<  in  length,  and 
a  terminal  segment  having  a  length  of  from  5  to  10//.  The  main  seg- 
ment has  a  central  fibrillated  axial  thread  which  is  continuous  with 
the  axial  thread  of  the  body.  This  is  enclosed  in  a  thin  cytoplasmic 
membrane  or  capsule  continuous  with  the  capsule  of  the  body.  This 
membrane,  inconspicuous  and  apparently  structureless  in  man, 
is  remarkably  developed  in  some  lower  forms,  e.g.,  the  membrana 
undulata  of  birds.  The  terminal  segment  consists  of  the  axial  thread 
alone.  The  motility  of  the  spermatozoon  depends  entirely  upon  the 
flagellate  movements  of  the  tail.  In  many  of  the  lower  animals  the 
spermatozoon  has  a  much  more  complicated  structure. 

Of  the  above-described  parts  of  the  spermatozoon  only  the  head  and 
tail  can  usually  be  differentiated,  except  by  the  use  of  special  methods  and 
very  high-power  objeectives. 

Development  of  the  Spermatozoa. — As  already  noted  in 
describing  the  testicle,  the  spermatozoa  are  developed  from  the  epithe- 
lial cells  of  the  seminiferous  tubules.  The  most  peripheral  of  the 
tubule  cells,  the  spermatogones  (Fig.  208,  sp  and  Fig.  209,  sp)  are  small 
round  cells  with  nuclei  rich  in  chromatin.  By  mitosis  the  s])ermato- 
gone  gives  rise  to  two  daughter  cells,  one  of  which  remains  at  the 
periphery  as  a  spermatogone,  while  the  other  takes  up  a  more  central 
position  as  a  spermatocyte  (Fig.  209,  sc  and  Fig.  211,  sc).  The  latter 
are  rather  large  spherical  cells,  whose  nuclei  show  very  distinct  chro- 
matin networks.  By  mitotic  di\ision  of  the  si^ermatocytes  of  the 
innermost  row  are  formed  the  spermatids  (Fig.  209,  st  and  Fig.  211,  st). 


THE  REPRODUCTIVE  SYSTEM. 


315 


These  are  small  spherical  cells,  which  line  the  lumen  of  the  tubule  and 
are  the  direct  progenitors  of  the  spermatozoa.  In  the  transformation 
of  spermatocyte  into  spermatid  an  extremely  important  change  takes 
place  in  the  nucleus.  This  consists  in  a  reduction  of  its  chromosomes  to 
one-half  the  number  specific  for  the  species  (page  52).  The  transfor- 
mation of  the  spermatid  into  the  spermatozoon  differs  somewhat  in 
different  animals  and  the  details  of  the  process  must  be  regarded  as  not 


Hea. 

Anterior  end  kncli       "~m^-^ 
Posterior  end  knob         ^ 

Body 
End  ring 


Tai 


r-    Head 


Anterior  end  knob 
Posterior  end  knob 

End  ring 


Nucleus 


Cytoplasm 
'.^  Proximal  centroscme 


Distal  centroscme 


Fig.  218. — Transformalion  of  a  Spermatid  into  a  Spermatozoon  (human).     Schematic. 

(Aleves,  Bonnet.) 


yet  definitely  determined.  The  nucleus  of  the  spermatid  first  becomes 
oval  in  shape,  and  its  chromosomes  become  condensed  into  a  small 
homogeneous  mass,  which  forms  the  head  of  the  spermatozoon. 
During  their  transformation  into  the  heads  of  the  spermatozoa,  the 
nuclei  of  the  spermatids  arrange  themselves  in  tufts  against  the  inner 
ends  of  the  cells  of  Sertoli.  This  compound  structure,  consisting  of  a 
Sertoli  cell  and  of  a  group  of  de\"eloping  spermatozoa  attached  to  its 


316  THE  ORGANS. 

central  end,  is  known  as  a  spermatoblast  (Fig.  211).  The  body  or 
middle  piece  of  the  spermatozoon  is  described  by  most  investigators 
as  derived  from  the  centrosome,  while  the  tail  is  a  derivative  of  the 
cytoplasm. 

The  details  of  the  transformation  of  the  spermatid  into  the  spermatozoon  are 
illustrated  in  Fig.  218.  The  centrosome  either  divides  completely,  forming  two 
centrosomes,  or  incompletely,  forming  a  dumb-bell-shaped  body.  The  nuclear 
material  becomes  very  compact  and  passes  to  one  end  of  the  cell,  forming  the  bulk 
of  the  head.  Both  centrosomes  help  to  form  the  body.  They  first  become  disk- 
shaped.  The  one  lying  nearer  the  center  of  the  cell  becomes  attached  to  the  posterior 
end  of  the  head  as  the  anterior  end-knob,  the  other  takes  a  position  a  little 
more  posteriorly  as  the  posterior  end-knob  and  from  it  grows  out  the  axial  filament. 
Some  of  this  centrosome  passes  to  the  posterior  limits  of  the  body  and  then  becomes 
the  end  ring.  As  the  two  parts  of  this  centrosome  separate  the  delicate  cytoplasm 
between  them  forms  the  spiral  fibres.  During  these  changes  the  axial  filament  has 
been  growing  and  projects  beyond  the  limits  of  the  cell.  Most  of  the  cytoplasm 
of  the  spermatid  is  not  used  in  the  formation  of  the  spermatozoon,  but  is  cast  off 
and  degenerates.  A  small  amount  is  used  for  the  sheath  of  the  body,  and  for  the 
galea  capitis.  The  sheath  of  the  main  part  of  the  filament  appears  to  develop  from 
the  filament  itself. 

The  significance  of  the  different  parts  of  the  spermatozoon  has  been  brought  out 
in  describing  its  development.  From  this  it  is  seen  that  the  spermatozoon,  like  the 
mature  ovum,  is  a  true  sexual  element  with  one-half  the  somatic  number  of  chromo- 
somes. The  head  and  body,  containing  the  chromatin  and  the  centrosomes,  are 
the  parts  of  the  spermatozoon  essential  to  fertilization.  The  acrosome  is  an  acces- 
sory which  in  some  forms  at  least  aids  the  spermatozoon  in  attaching  itself  to  and 
in  entering  the  ovum.  The  tail  is  an  accessory  structure  which  provides  motion, 
enabling  the  spermatozoon  to  move  about  freely  in  the  semen  and  in  the  fluids  of 
the  female  generative  tract.  Considering  ther  minuteness,  their  speed  is  consider- 
able, having  been  estimated  at  from  1.5  to  3.5  mm.  per  minute;  enough  to  allow 
them  to  ascend  through  uterus  and  oviduct  against  the  adverse  action  of  the  cilia. 
When  in  a  favorable  environment,  such  as  the  fluids  of  the  female  generative  tract, 
the  spermatozoon  is  capable  of  living  for  some  time  after  leaving  the  testicle.  Living 
spermatozoa  have  been  found  in  the  uterus  or  tubes  one  to  three  and  a  half  weeks 
after  coitus. 

TECHNIC. 

(i)  For  the  study  of  the  general  topography  of  the  testis,  remove  the  testis  of 
a  new-born  child,  make  a  deep  incision  through  the  tunica  albuginea  in  order  to 
allow  the  fixative  to  penetrate  quickly,  and  fix  in  formalin-Miiller's  fluid  (technic  5, 
p.  7).  Antero-po.sterior  longitudinal  sections  through  the  entire  organ  and  in- 
cluding the  epididymis  should  be  stained  with  haematoxylin-picro-acid-fuchsin 
Ctechnic  3,  p.  19)  or  with  hicmatoxylin-eosin  (technic  i,  p.  18)  and  mounted  in 
balsam. 

(2)  The  testis  of  a  young  adult  is  removed  as  soon  after  death  as  possible,  is 


THE  REPRODUCTIVE  SYSTEM.  317 

cut  into  thin  transverse  slices,  which  include  the  epididymis,  and  is  iixed  in  fornia- 
lin-Mliller's  or  in  Zenker's  fluid  (technic  9,  p.  8).  Select  a  slice  which  includes  the 
head  of  the  epididymis,  cut  away  the  anterior  half  or  two-thirds  of  the  testis 
proper  in  order  to  reduce  the  size  of  the  block,  and,  after  the  usual  hardening 
and  embedding,  cut  thin  sections  through  the  remaining  posterior  portion  of 
the  testis,  the  mediastinum,  and  epididymis.  Stain  with  hasmatoxylin-eosin 
(technic    i,    p.   18)  and  mount  in  balsam. 

(3)  For  the  study  of  spermatogenesis  fix  a  mouse's  testis  in  chrome-acetic- 
osmic  mixture  (technic  7,  p.  7).  Harden  in  alcohol  and  mount  thin  unstained 
sections  in  balsam  or  in  glycerin. 

(4)  Spermatozoa. — Human  spermatozoa  may  be  examined  fresh  in  warm  nor- 
mal saline  solution  or  fixed  in  saturated  aqueous  solution  of  picric  acid  and  mounted 
in  glycerin.  Mammalian  spermatozoa  may  be  obtained  from  the  vagina  after 
intercourse,  or  by  incision  into  the  head  of  the  epididymis.  Technic  same  as  for 
human. 

(5)  A  portion  of  the  vas  deferens  is  usually  removed  with  the  testis  and  may  be 
subjected  to  technic  (2)  above.  Transverse  sections  are  stained  with  hsematoxylin- 
eosin  and  mounted  in  balsam. 


The  Prostate  Gland. 

The  prostate  is  described  by  some  as  a  compound  tubular,  by 
others  as  a  compound  alveolar  gland.  It  is  perhaps  best  regarded 
as  a  collection  of  simple  branched  tubular  glands  with  dilated  termi- 
nal tubules.  These  number  from  forty  to  fifty,  and  their  ducts  con- 
verge to  form  about  tw^enty  main  ducts,  which  open  into  the  urethra. 
The  gland  is  surrounded  by  a  capsule  of  fibro-elastic  tissue  and  smooth 
muscle  cells,  the  muscle  cells  predominating.  From  the  capsule 
broad  traheculcE  of  the  same  structure  as  the  capsule  pass  into  the 
gland.  The  amount  of  connective  tissue  is  large.  It  is  less  in  the 
prostate  of  the  young  than  of  the  old.  The  hypertrophied  pre  state 
of  age  is  due  mainly  to  an  increase  in  the  connective-tissue  elements. 
The  tubules  have  wide  lumina  and  are  lined  with  simple  cuboidal 
epithelium  of  the  serous  type,  resting  upon  a  delicate  basement  mem- 
brane (Fig.  219).  Less  commonly  the  epithelium  is  pseudo-stratified. 
The  ducts  are  lined  with  simple  columnar  epithelium  until  near  their 
terminations,  where  they  are  Hned  with  transitional  epithelium  similar 
to  that  lining  the  urethra.  Peculiar  concentrically  laminated  bodies. 
crescentic  corpuscles,  or  corpora  amylacea,  are  frequently  present  in  the 
terminal  tubules  (Fig.  219,  c).  They  are  more  numerous  after  middle 
life.      Through  the  prostate  runs  the  prostatic  portion  of  the  urethra. 

Within    the    prostate    is    found    the    vcsiciila    prostatica    (ittriciihis 


318  THE  ORGANS. 

prostaticus — uterus  masculinus).  It  represents  the  remains  of  a  foe- 
tal structure,  the  MiiUerian  duct  and  consists  of  a  blind  sac  with  folded 
mucous  membrane  lined  with  a  two-rowed  ciliated  epithelium  which 
dips  down  to  form  short  tubular  glands.  The  prostatic  secretion 
is  serous. 

The  blood-vessels  of  the  prostate  ramify  in  the  capsule  and  tra- 
beculae.  The  small  arteries  give  rise  to  a  capillary  network  which 
surrounds  the  gland  tubules.  From  these  arise  small  veins,  which 
accompany  the  arteries  in  the  septa  and  unite  to  form  venous  plexuses 
in  the  capsule. 

a 


•     jr     /  .     '-  >', 


b/----'  "  -  ^ 


Fig.  219. — Section  of  Human  Prostate.      X  150.     (Tcchnic  i,  p.  .^ig.)     a,  Epithelium  of 
tubule;  h,  interstitial  connective  tissue;  c,  corpora  amylacea. 

The  lymphatics  begin  as  blind  clefts  in  the  trabecute  and  follow 
the  general  course  of  the  blood-vessels. 

Nerves, — Small  groups  of  sympathetic  ganglion  cells  are  found  in 
the  larger  trabeculae  and  beneath  the  capsule.  Axones  of  these  cells 
pass  to  the  smooth  muscle  of  the  traljeculae  and  of  the  walls  of  the 
blood-vessels.  Their  mode  of  termination  is  not  known.  Timofeew 
describes  afferent  medullatcd  fibres  ending  within  capsular  structures 
of  flat  nucleated  cells.  Two  kinds  of  fibres  pass  to  each  capsule: 
one  a  large  medullated  fibre  which  loses  its  sheath  and  gives  rise 
within  the  capsule  to  several  flat  fibres  with  serrated  edges,  the  other 
small  medullated  fibres  which  lose  their  sheaths  and  split  up  into 


THE  REPRODUCTIVE  SYSTEM. 


319 


small  varicose  fibrils  which  form  a  network  around  the  terminals  of 
the  large  fibre. 

Cowper's  Glands. 

The  bulbo-urethral  glands,  or  glands  of  Cowper,  are  small,  com- 
pound tubular  glands.  Both  tubules  and  ducts  are  irregular  in  di- 
ameter so  that  some  of  them  have  more  the  character  of  alveoli  than 
of  tubules.  They  are  lined  with  mucous  cells.  The  smaller  ducts  are 
lined  with  simple  cuboidal  epithelium.  They  unite  to  form  two 
main  excretory  ducts  which  open  into  the  urethra  and  are  lined  with 
stratified  columnar  epithelium  consisting  of  two  or  three  layers  of  cells. 
In  the  main  duct,  as  well  as  in  its  branches,  smooth  muscle  occurs. 

TECHNIC, 

(i)  Fix  small  pieces  of  the  prostate  of  a  young  man  in  formalin-Miiller's  fluid 
(technic  5,  p.  7).  Stain  sections  with  htematoxylin-eosin  (technic  i,  p.  18)  and 
mount  in  balsam. 

(2)  The  prostate  of  an  old  man  should  be  treated  with  the  same  technic  and 
compared  with  the  above. 

(3)  Cowper's  glands.     Same  technic  as  prostate  (i). 

The  Penis. 

The  penis  consists  largely  of  three  long  cyhndrical  bodies,  the 
corpus  spongiosum  and  the  two  corpora  cavernosa.  The  latter  lie  side 
by  side,  dorsally,  while  the  corpus  ^ 

spongiosum  occupies  a  medial 
ventral  position  (Fig.  220).  All 
three  are  enclosed  in  a  common 
connective-tissue  capsule  which 
is  loosely  attached  to  the  o\ev- 
lying  skin.  In  addition  each 
corpus  has  its  own  special  cap- 
sule or  tunica  albuginea,  about  a 
millimetre  in  thickness,  and 
composed  of  dense  connective 
tissue  containing  many  elastic 
fibres. 

The  corpus  spongiosum  and 
corpora  cai'crnosa  have  essentially 
the  same  structure,  being  composed  of  so-called  erectile  tissue  (Fig.  221). 
This  consists  of  thick  trabeculae  of  intermingled  fibro-elastic  tissue  and 
bundles  of  sm.ooth  muscle  cells,  which  anastomose  to  form  a  coarse 


Fig.  220. — Tran.s\er>e  Scnion  through  Human 
Penis,  a.  Skin:  b,  subcutaneous  tissue;  c, 
fibrous  tunic;  d,  dorsal  vein;  e,  corpora  cav- 
ernosa: /,  corpus  spongiosum;  g,  urethra. 


320  THE  ORGANS. 

meshed  network,  the  spaces  of  which  are  hned  with  endothehum. 
The  spaces  are  known  as  cavernous  sinuses,  and  communicate  with 
one  another,  and  with  the  blood-vessels  of  the  penis.  In  the  flaccid 
condition  of  the  organ  these  sinuses  are  empty  and  their  sides  are  in 
apposition.  In  erection  these  sinuses  become  filled  with  venous  blood. 
The  arteries  have  thick  muscular  walls  and  run  in  the  septa.  A 
few  of  them  open  directly  into  the  venous  sinuses.  Most  of  them 
give  rise  to  a  superficial  capillary  network  beneath  the  tunica  albu- 
ginea.     From  this  capillary  plexus  the  blood  passes  into  a  plexus  of 


\--  ■'  ■' 
!£"■■:- 


r/ 


■M^'^ 


Fig.  221. — Erectile  Tissue  of  Corpus  Spongiosum  of  Human  Penis.  X  60.  a, 
Trabecule  of  connective  tissue  and  smooth  muscle;  b,  cavernous  sinuses;  c,  groups  of 
leucocytes  in  sinus. 

broader  venous  channels  in  the  periphery  of  the  erectile  tissue,  and 
these  in  turn  communicate  with  the  cavernous  sinuses.  The  usual 
direct  anastomoses  between  arterial  and  venous  capillaries  also  occur. 
The  blood  may  therefore  pass  either  through  the  usual  course — arte- 
ries, capillaries,  veins — or,  under  certain  conditions,  may  pass  through 
the  cavernous  sinuses.  This  determines  the  flaccid  or  the  erect  con- 
dition of  the  organ.  The  veins  arise  partly  from  the  capillaries  and 
partly  from  the  cavernous  sinuses.  They  pass  through  the  tunica 
albuginea  and  empty  into  the  dorsal  vein  of  the  penis  (Fig.  220).  In 
the  corpus  spongiosum  there  is  probably  no  direct  opening  of  arteries 
into  sinuses.     Both  trabeculse  and  sinuses  are  also  smaller. 

Of  the  lymphatics  of  the  jjenis  Httle  definite  is  known. 

The  nerve  endings,  according  to  Dogicl,  consist  of:  (a)  free  sensory 
endings,  (b)  deeply  situated  genital  corpuscles,   (c)  Pacinian  corpus- 


THE  REPRODUCTI\E  SYSTEM. 


321 


10  f- 


cles  and  Krause's  end-bulbs  in  the  more  superficial  connective  tissue, 
and  (d)  Meissner's  corpuscles  in  the  papillae.  (For  details  see  pages 
387  and  388.) 

The  glans  penis  consists  of  erectile  tissue  similar  in  structure  to 
that  of  the  corpus  cavernosum,  except  that  the  venous  spaces  are 
smaller  and  more  regular.  The  mucous  membrane  is  very  closely  at- 
tached to  the  fibrous  sheath  of  the  ^ 
underlying  erectile  tissue.  A  few  ,  ' 
small  sebaceous  glands,  uncon-  I 
nected  with  hairs — the  glands  of 
Tyson — are  found  in  the  mucous 
membrane  of  the  base  of  the  glans 
penis. 

The  prepuce  is  a  fold  of  skin 
which  overlies  the  glans  penis.  Its 
inner  surface  is  lined  with  mucous 
membrane. 


ff.&S3 


^■■> 


-  d 


Fig. 


Fig.  223. 


Fig.  222. — From  Transverse  Section  of  Urethra  and  Corpus  Spongiosum,  including 
Mucous  Membrane  and  part  of  Submucosa.  X  15.  The  dari<.  spots  represent  the 
cavernous  veins. 

Fig.  223.^ — Vertical  Section  through  Portion  of  Wall  of  Human  Male  Urethra.  X  350. 
A,  Mucous  membrane;  B,  submucosa ;  a,  epithelium;  b,  stroma;  c,  cavernous  veins:  d,  con- 
nective tissue  of  submucosa. 


The  Urethra/ 

The  MALE  URETHRA  is  divided  into  three  parts — prostatic,  mem- 
branous, and  penile.     The  wall  of  the  urethra  consists  of  three  coats 

'  The  female  urethra,  while  not  so  distinctly  divisible  into  sections,  presents  essentially 
the  same  structure  as  the  male  urethra.  The  epithelium  begins  at  the  bladder  as  stratified 
squamous  of  the  transitional  type,  changes  to  a  two-layered  stratified  or  pseudostratified, 
and  finally  passes  over  into  stratified  squamous  near  the  urethral  opening.  Glands  of 
Littre  are  present,  but  are  fewer  than  in  the  male. 


322  THE  ORGANS. 

— mucous,  submucous,  and  muscular.  The  structure  of  the  wall 
differs  in  the  different  parts  of  the  urethra. 

The  mucous  membra?ie  (Fig.  223)  consists  of  epithelium  and  stroma. 
The  epithelium  of  the  prostatic  part  is  stratified  squamous  (transi- 
tional), resembling  that  of  the  bladder.  In  the  membranous  part  it 
is  stratified  columnar  or  pseudostratified.  In  the  penile  portion  it 
is  pseudostratified  up  to  the  fossa  navicularis,  where  it  changes  to 
stratified  squamous.  The  epithelium  rests  upon  a  basement  mem- 
brane, beneath  which  is  a  thin  stroma  rich  in  elastic  fibres  and  hav- 
ing papillae  which  are  especially  prominent  in  the  terminal  dilated 
portion  of  the  urethra,  the  fossa  navicularis.  The  stroma  merges 
without  distinct  demarcation  into  the  submucosa. 

The  submucosa  consists  of  connective  tissue  and,  in  the  penile 
portion,  of  more  or  less  longitudinally  disposed  smooth  muscle.  It 
contains  a  dense  network  of  veins — cavernous  veins — which  give  it  the 
character  of  erectile  tissue  (Fig.  223). 

The  muscular  coat  is  thickest  in  the  prostatic  and  membranous 
portions.  Here  it  consists  of  a  thin  inner  longitudinal  and  a  thicker 
outer  circular  layer.  A  definite  muscular  wall  ceases  at  the  beginning 
of  the  penile  portion,  although  circularly  disposed  smooth  muscle  cells 
are  found  in  the  outer  part  of  the  submucosa  of  the  penile  urethra. 

Throughout  the  mucosa  of  the  entire  urethra,  but  most  numerous 
in  the  penile  portion,  are  simple  branched  tubular  mucous  glands, 
the  glands  of  Littre.  They  are  lined  with  columnar  epithelium  and 
the  longer  extend  into  the  submucosa. 


TECHNIC. 

ii)  For  the  study  of  the  general  topography  of  the  penis,  remove  the  slcin  from 
the  organ  and  cut  into  transverse  slices  about  0.5  cm.  in  thickness.  Fix  in  forma- 
lin-Miiller's  fluid  (technic  5,  j).  7),  cut  rather  thick  sections  across  the  entire 
penis,  stain  with  hsematoxylin-picro-acid-fuchsin  (technic  3,  p.  19)  or  with  hiema- 
toxylin-eosin  (technic  i,  p.  18)  and  mount  in  balsam. 

(2)  For  the  study  of  the  structure  of  the  penile  portion  of  the  urethra  and  of 
the  erectile  tissue  of  the  corpus  spongiosum,  cut  away  the  corpora  cavernosa,  leav- 
ing only  the  corpus  spjongiosum  and  contained  urethra,  and  treat  as  above.  Sec- 
tions should  be  thin  and  stained  with  haematoxylin-eosin. 

(3)  The  same  technic  is  to  be  used  for  the  membranous  and  prostatic  portions 
of  the  urethra. 


THE  REPRODUCTRE  SYSTEM. 


323 


II.  FEMALE  ORGANS. 
The  Ovary. 

The  ovary  is  classed  as  one  of  the  ductless  glands.  Its  specific 
secretion  is  the  ovum.  The  ovary  has  no  duct  system  which  is  directly 
continuous  with  its  structure.  In  place  of  this  it  is  pro\ided  with 
what  may  be  considered  to  be  a  highly  specialized  disconnected 
excretory  duct — the  oviduct  or  Fallopian  tube — which  serves  for  the 
transmission  of  its  secretion  to  the  uterus. 

On  one  side  the  ovary  is  attached  by  a  broad  base,  the  hilion,  to 
the  broad  ligament.     Elsewhere  the  surface  of  the  ovarv  is  covered 


Fig.  224. — Ovary  opened  by  Longitudinal  Incision.  Ovum  has  Escaped  through 
Tear  in  Surface.  Cavity  of  follicle  filled  with  blood  clot  (corpus  haemorrhagicum)  and 
irregular  projections  composed  of  lutein  cells.     (Kollmann's  Atlas.) 


by  a  modified  peritoneum.  At  the  hilum  the  tissues  of  the  broad 
ligament  pass  into  the  ovary  and  spread  out  there  to  form  the  ovarian 
stroma.  This  consists  of  fibrous  connective  tissue  rich  in  elastic  fibres 
and  containing  many  smooth  muscle  cells.  In  the  deeper  central 
portion  of  the  organ,  stroma  alone  is  found.  Here  it  contains  many 
large  blood-vessels,  and  constitutes  the  medulla  or  zmia  vasculosa  of 
the  ovary  (Fig.  225,  2).  From  the  medulla  the  stroma  radiates  toward 
the  surface  of  the  o\"ary  and  becomes  interspersed  with  glandular 
elements  forming  the  ovarian  cortex  (Fig.  225,  3,  3').  At  the  surface 
of  the  ovary,  just  beneath  the  peritoneum,  the  stroma  forms  a  rather 


324 


THE  ORGANS. 


dense  layer  of  fibrous  tissue,  the  tunica  albuglnea.  At  the  margin  of 
the  peritoneal  surface  of  the  ovary  the  connective  tissue  of  the  perit- 
oneum becomes  continuous  with  the  stroma  of  the  ovary,  while  the 
flat  mesothelium  of  the  general  peritoneum  is  replaced  by  a  single 
layer  of  cuboidal  cells,  which  covers  the  surface  of  the  ovary  and  is 
known  from  its  function  as  the  germinal  epithelium  (Fig.  226,  he). 
The  parenchyma  or  secreting  portion  of  the  ovary  consists  of  peculiar 
glandular  elements,  the  Graafian  follicles. 


'^^'^^:£kl 


/m 


m 

M 


'^m^m 


■"-^KjJ'f: 


~^^%:\  ,x;^o>A\v.V 


Fig.  225. — Semidiagrammatic  Drawing  of  Part  of  Cortex  and  Medulla  of  Cat's  Ovary. 
(From  Schron,  in  Quain's  "Anatomy.")  i,  Germinal  epithelium,  beneath  which  is  3,  the 
tunica  albuginea;  2,  medulla,  containing  large  blood-vessels,  4;  2,2',  fibrous  stroma, 
arranged  around  mature  Graafian  follicle  as  its  theca  foUiculi;  3',  stroma  of  cortex;  5,  small 
(primitive)  Graafian  follicles  near  surface;  6,  same  deeper  in  cortex;  7,  later  stage  of 
Graafian  follicle,  beginning  of  cavity;  8  and  8',  still  later  stages  in  development  of  follicle; 
9,  mature  follicle;  a,  stratum  granulosum;  b,  germ  hill;  c,  ovum;  d,  nucleus  (germinal 
vesicle);  e,  nucleolus  (germinal  spot). 

The  structure  of  the  Graafian  follicle  can  be  best  appreciated  by 
studying  its  development.  The  follicles  originate  from  the  germinal 
epithelium  during  foetal  life.  At  this  time  the  germinal  epithehum 
is  proliferating,  and  certain  of  its  cells  differentiate  into  larger  spherical 
cells — primitive  ova  (Fig.  226,  op) .  The  primitive  ova  pass  downinto  the 
stroma  accompanied  ]jy  a  considerable  number  of  the  undifferentiated 
cells  of  the  germinal  epithelium.  A  cord-like  mass  of  cells  is  thus 
formed,  extending  from  the  surface  into  the  stroma.  This  is 
known  as  PJlilger's  egg  cord  (Fig.  226).  Each  cord  usually  contains 
several  ova.  In  some  cases  the  differentiation  of  the  ova  cells  does 
not  occur  uijon  the  surface  but  in  the  cords  after  they  have  extended 


THE  REPRODUCTR  E  SYSTEM.  325 

down  from  the  surface.  The  connection  of  the  cord  with  the  surface 
epithehum  is  next  broken  so  that  each  cord  becomes  completely  sur- 
rounded Ijy  stroma.  It  is  now  known  as  an  eggnest  (Fig.  226).  During 
this  process,  proliferation  of  the  epithelial  cells  of  the  cords  and  nests  has 
been  going  on,  and  each  ovum  surrounded  by  a  layer  of  epithelial  cells 
becomes  separated  from  its  neighbors  (Fig.  226,  fp).  This  central 
ovum  surrounded  by  a  single  layer  of  epithelial  cells  (follicular  cells) 
is  the  primitive  Graafian  follicle  (Fig.  226,  fp,  Fig.  227,  and  Fig.  228,  a). 
Rarely  a  follicle  may  contain  more  than  one  ovum,  of  which,  however, 


„-,      at      -   i»    %     ^  ,     10  ^^  o 


-.»  .-   -is 

X         ^    ■   ^^  . 

Fig.  226. — From  Transverse  Section  of  Ovary  of  New-born  Child.  X  280  (Sobotta). 
Shows  primitive  ova  in  germinal  epithelium;  Pfliiger's  egg  cords  and  nests  of  cells;  c, 
capillaries;  he,  germinal  epithelium;  sir,  stroma;  fp,  primitive  follicles;  op,  primitive  ova. 


only  one  goes  on  to  maturity,  the  others  degenerating.  The  follicle 
increases  in  size,  mainly  on  account  of  proliferation  of  the  follicular 
cells,  which  soon  form  se\'eral  layers  instead  of  a  single  layer,  but  also 
partly  on  account  of  growth  of  the  ovum  itself  (Fig.  228).  The  latter 
now  lea^"es  the  centre  of  the  follicle  and  takes  up  an  eccentric  position. 
At  the  same  time  a  cavity  (or  several  small  ca\'ities  which  later  unite) 
appears  near  the  centre  of  the  follicle  (Fig.  228,  e  and  Fig.  225,  7). 
This  is  filled  with  fluid  which  seems  to  be  in  part  a  secretion  of  the 
follicular  cells,  in  part  a  result  of  their  disintegration.  The  cavity  is 
known  as  the  follicular  cai'ily  or  anlnnn.  the  fluid  as  the  liquor  foil iciili. 


326 


THE  ORGANS. 


Lining  the  follicular  cavity  are  several  rows  of  follicular  cells  with 
granular  protoplasm — the  stratum  granulosum.  With  increase  in  the 
liquor  folliculi  the  ovum  becomes  still  further  pressed  to  one  side  of  the 
folhcle,  where,  surrounded  by  an  accumulation  of  folHcular  cells,  it 
forms  a  distinct  projection  into  the  cavity  (Fig.  230,  and  Fig.  225, 


^  Fig. 
and  von 
d,  ovum; 
follicle. 


227. — Vertical  Section  thn;ujrh  C(jrtex  of  Ovary  of  Young  Girl.  X  igo.  (Bohm 
Davidoff.)  a,  Germinal  epithelium;  h,  tunica  albuginea;  c,  follicular  epithelium; 
e,  primitive  Graafian  follicles  in  ovarian  cortex;  /,  granular  layer  of  large  Graafian 


8  and  cj).  I'his  is  known  as  the  germ  hill  {discus  proligcrus — cumulus 
ovigerus).  The  cells  of  the  germ  hill  nearest  the  ovum  Ijecome  col- 
umnar and  arranged  in  a  regular  single  layer  around  the  ovum — 
the  corona  radiata  (Fig.  231).  The  ovarian  stroma  immediately  sur- 
rounding the  (jraafian  follicle  becomes  somewhat  modified  to  form 
a  sheath  for  the  follicle — the  the ca  folliculi  (Fig.  229).  This  consists 
of  two  layers,'  an  outer  more  dense  fibrous  layer,  the  tunica  fibrosa, 


THE  REPRODL'CTIVE  SYSTEM.  327 

and  an  inner  more  cellular  and  vascular,  the  tunica  vasculosa.  Be- 
tween the  theca  folliculi  and  the  stratum  granulosum  is  an  apparently 
structureless  basement  membrane. 

While  these  changes  are  taking  place  in  the  follicle,  the  ovum  is 
also  undergoing  development.  The  ovum  of  the  primitive  follicle  is 
a  spherical  cell,  having  a  diameter  of  from  40  to  yo/t  and  the  structure 
of  a  typical  cell.  The  nucleus  or  germinal  vesicle  (so  called  on  account 
of  the  part  it  takes  in  reproduction)  is  about  half  the  diameter  of  the 
cell,  and  is  spherical  and  centrally  placed  (Fig.  228).     It  is  surrounded 


i-'.- 1::.  V  :.  v''  -■- 


Fig.  228. — From  Section  through  Cortex  of  Ape's  Ovary.  X  150.  (Szymonowicz.) 
a,  Primitive  follicle;  h,  ovum,  with  nucleus  and  nucleolus;  c,  zona  pellucida;  d,  follicular 
epithelium;  e,  follicular  cavity;/,  ovarian  stroma;  g,  blood-vessel  in  stroma. 

by  a  double-contoured  nuclear  membrane,  and  contains  a  distinct 
chromatic  network  and  nucleolus  or  germinal  spot.  The  cytoplasm 
is  quite  easily  differentiated  into  a  spongioplasm  network  and  a  homo- 
geneous hyaloplasm.  Such  ova  are  present  in  all  active  ovaries,  i.e., 
during  the  childbearing  period,  but  are  especially  numerous  in  the 
ovary  of  the  infant  and  child  (Fig.  227.) 

With  the  development  of  the  follicle  the  ovum  increases  in  size 
and  becomes  surrounded  by  a  clear  membrane,  the  zona  pellucida, 
belie\"ed  by  some  to  be  a  cuticular  formation  deposited  by  the  egg  cell, 
by  others  to  be  a  product  of  the  surrounding  follicular  cells.  Minute 
canals  extend  into  the  zona  pellucida  from  its  outer  surface.  These 
contain  processes  of  the  cells  of  the  corona  radiata.  A  narrow  cleft, 
the  periviteUinc  space,  has  been  described  as  se])arating  the  o\'um  from 
the  zona   jjellucida.     During  the  growth  of  the  o\um  its  cyto])lasm 


328  THE  ORGANS. 

becomes  coarsely  granular  from  the  development  of  yolk  or  deutoplasm 
granules  (Fig.  231).  Immediately  surrounding  the  nucleus,  and  just 
beneath  the  zona  pellucida,  the  egg  protoplasm  is  fairly  free  from  yolk 
granules. 

The  further  maturation  of  the  ovum,  which  is  necessary  before  the 
egg  cell  is  in  condition  to  be  fertilized,  consists  in  changes  in  the 
chromatic  elements  of  the  nucleus,  v^hich  result  in  the  extrusion  of 
the  polar  bodies,  and  apparently  have  as  their  main  object  the  reduction 
in  number  of  chromosomes  to  one-half  the  number  characteristic  of 
the  species.     This  process  has  been  described  (page  53).     In  many 


;'>A  . 

'^>!^  • 

.^ 

i'*  Kj^" 

"l''s^- 

-*5ii 

% 

''^V;  '    '. 

'*^^. 

^ 

■:^M0^' 


—  / 


Fig.  22Q. — Section  through  Graafian  Follicle  of  Ape's  Ovary.  X  90.  (Szymonowicz.) 
Later  stage  of  development  than  Fig.  228.  a,  Germ  hill ;  b,  ovum  with  clear  zona  pellucida, 
germinal  vesicle,  and  germinal  spot;  d,  follicular  epithelium  (membrana  granulosa);  e, 
follicular  cavity;/,  theca  folliculi;  g,  blood-vessel. 

of  the  lower  animals  maturation  of  the  ovum  is  completed  outside  the 
ovary.  In  man  and  the  higher  animals  the  entire  process  takes  place 
within  the  o\'ary,  the  second  polar  body  being  extruded  just  before  the 
escape  of  the  o\'um  from  its  follicle. 

The  youngest  of  the  Graafian  follicles  are  found  just  under  the 
tunica  albuginea  near  the  germinal  epithelium,  from  which  they 
originate  (Fig.  225,  5).  As  the  follicle  matures  it  passes  deeper  into 
the  cortex.  With  complete  maturity  the  follicle  usually  assumes 
macroscopic  proportions — 8  to  12  mm. — and  often  occupies  the  entire 
thickness  of  the  cortex,  its  theca  at  one  point  touching  the  tunica 
albuginea.  Thinning  of  the  follicular  wall  nearest  the  surface  of  the 
ovary  next  takes  place  dig.  232),  while  at  the  same  time  an  increase  in 


THE  REPRODUCTRE  SYSTEM. 


;^29 


the  liquor  tolliculi  determines  increased  intrafoUicular  pressure.  This 
results  in  rupture  of  the  Graaiian  follicle  and  the  discharge  of  its 
ovum,  together  with  the  liquor  folliculi  and  some  of  the  follicular  cells. 
An  escape  of  blood  into  the  follicle  from  the  torn  vessels  of  the 
theca  always  accompanies  the  discharge  of  the  ovum.  The  follicle 
again  becomes  a  closed  cavity,  while  the  contained  blood  clot  becomes 


Fig.  2.:;o — Graafian  Follicle  and  Contained  Ovum  of  Cat:  directly  reproduced  from  a 
photograph  of  a  preparation  by  Dahlgren.  X  235.  (From  "The  Cell  in  Development 
and  Inheritance,"  Prof.  E.  B.  Wilson;  The  Macmillan  Company,  publishers.)  The  ovum 
is  seen  lying  in  the  Graafian  follicle  within  the  germ  hill,  the  cells  of  the  latter  immediately 
surrounding  the  ovum  forming  the  corona  radiata.  The  clear  zone  within  the  corona  is  the 
zona  pellucida,  within  which  are  the  egg  protoplasm,  nucleus,  and  nucleolus.  Encircling 
the  follicle  is  the  connective  tissue  of  the  theca  folliculi. 


organized  by  the  ingrowth  of  vessels  from  the  theca,  to  form  the  corpus 
hcEmorrhagkum  (Fig.  233),  which  represents  the  earliest  stage  in  the 
development  of  the  corpus  hitcuni. 

The  corpus  lutcum  (Fig.  234),  which  replaces  the  corpus  haemor- 
rhagicum,  consists  of  large  yellow  cells — lutein  cells — and  of  connective 
tissue.  The  latter  with  its  blood-vessels  is  derived  from  the  inner 
layer  of  the  theca.  The  origin  of  the  lutein  cells  is  not  clear.  They 
are  described  bv  some  as  deri\"ed  from  the  connccti\"e-tissue  cells  of 


330 


THE  ORGANS. 


the  theca;  by  others  as  the  result  of  prohferation  of  the  cells  of  the 
stratum  granulosum.  The  cells  have  a  yellow  color  from  the  presence 
of  fatty  (lutein)  granules  in  their  protoplasm,  and  it  is  to  these  granules 
that  the  characteristic  yellow  color  of  the  corpus  luteum  is  due.  A 
definite  cellular  structure  with  a  supporting  connective-tissue  framework 
thus  replaces  the  corpus  hasmorrhagicum,  remains  of  which  are  usually 


Fig.  231.— From  a  Scciion  of  a  Human  Ovum.  Seclion  taken  from  the  ovary  of  a 
12  year  old  girl.  The  ovum  lies  in  a  large  mature  Graafian  follicle  and  is  surrounded 
by  the  cells  of  the  "germ  hill "  (the  inner  edge  of  which  is  shown  in  the  upper  left-hand 
corner  of  the  figure).     Photograph.     (Bailey  and  Miller). 

present  in  the  shape  of  orange-colored  crystals  of  hsematoidin.  By 
degeneration  and  subsequent  absorption  of  its  tissues  the  corpus 
luteum  becomes  gradually  reduced  in  size,  loses  its  yellow  color,  and  is 
then  known  as  the  corpus  albicans.  This  also  is  mostly  absorbed,  being 
finally  represented  merely  by  a  small  area  of  fibrous  tissue. 

Corpora  lutea  are  divided  into  true  corpora  lulea  (corjjora  lutea 
vera  or  corpora  lutea  of  pregnancy)  and  false  corpora  lutea  (corpora 


THE  REPRODUCTIVE  SYSTEM. 


331 


r^¥// 


Germinal 
einthelium 


^xi*---; 


Tunica  albugmea 


p/      ' 


Germ  hill 


Theca  foUicu 


h      tv.V:^*^ 

with  o\-um      (vascular  lai  ers) 2t_.  »\\  *{«    ^v 

^-   wj  I 

Theca  folliculi  (fibrous  la\  er"*  - —  '[,    'M  S^i 

Stratum  granulosum 


Y\G.i^2. From  Section  of  Human  Ovar\-,  showing  mature  Graatian  follicle  ready 

to  rupture.      (KoUmann's  Atlas.) 


Lutein  cells     >^^-^,,;>e"^. 


^jii^^^^u^'^'%~-2^  Point  ot  luptur 


Corpus  hEemorrhagicum- 


Blood  vessel  of  theca 


'n  ' 


-Cavitv  of  foUicle 


-Theca  folliculi 


,rr&- 


:anan  stroma 


Stratum  granulosum 


Fig.  233. — From  Section  of  Human  Ovary,  showing  early  stage  in  formation 
of  Corpus  Luteum.   (KoUmann's  .Atlas.) 


332 


THE  ORGANS. 


lutea  spuria).  The  former  replace  follicles  whose  ova  have  under- 
gone fertilization,  the  latter,  follicles  whose  ova  have  not  been  ferti- 
lized. The  structure  of  both  is  similar,  but  the  true  corpus  luteum 
is  larger,  and  both  it  and  its  corpus  albicans  are  slower  in  passing 
through  their  retrogressive  changes,  thus  remaining  much  longer  in 
the  ovary. 

While  the  function  of  the  curpus  luteum  is  not  known,  the  recent 
experiments  of  Fraenkel  seem  to  be  confirmatory  of  the  theory  ad- 

Point  of  rupture. 


Blood-vessel 
of  theca 


Connective 
tissue 


Remnant  of 
corpus 
hasmorrhagicum 


Lutein  cells 


Connective 
tissue  from 
theca 


Theca  folliculi 


Blood-vessels 
of  theca 


Fig.  234. — P'njm  Section  of  Human  Ovary,  showing  later  stage  of  Corpus  Luteum 
than  Fig.  233.      (Kohmann's  Atlas.) 


\'anccd  by  Jiorn,  that  the  corpus  luteum  is  a  gland  having  an  internal 
secretion,  which  ajjpears  to  have  some  influence  u])on  the  attachment 
of  the  fecundated  ovum  to  the  uterus  and  upon  its  nutrition  during 
the  first  few  weeks  of  its  develo])ment.     According  to  Fraenkel  the 

cor]jus  luteum  is  a  perioflically  rejux'enated  ox'arian  gland,  which 
gives  to  the  uterus  a  cyclic  nutritional  iminilse,  which  ];repares  it  for 


THE  REPRODUCTR'E  SYSTEM.  333 

the  implantation  of  the  o\'um  or  favors  menstruation  whenever  the 
ovum  is  not  fertihzed. 

Of  the  large  number  of  ova — estimated  at  seventy-two  thousand 
in  the  human  ovaries — only  comparatively  few,  according  to  Henle 
about  four  hundred,  reach  maturity.  The  majority  undergo,  together 
with  their  follicles,  retrogressive  changes  known  as  atresia  of  the 
follicle.  The  nucleus  of  the  ovum,  as  well  as  the  nuclei  of  the  fol- 
licular cells,  passes  through  a  series  of  chromatolytic  changes,  or  in 
some  cases  apparently  simply  atrophies.  The  cell  bodies  undergo 
fatty  or  albuminous  degeneration  and  the  cell  becomes  reduced  to  a 
homogeneous  mass,  which  is  finally  absorbed,  leaving  in  its  place  a 
connective-tissue  scar,  probably  the  remains  of  the  theca  folliculi. 

Blood-vessels. — The  arteries,  branches  of  the  ovarian  and  uterine, 
enter  the  ovary  at  the  hilum  and  ramify  in  the  medulla.  From  these 
are  given  off  branches  which  pass  to  the  cortex  and  end  in  a  capil- 
lary network  in  the  tunica  albuginea.  In  the  outer  layer  of  the  theca 
folliculi  the  capillaries  form  a  wide-meshed  network,  which  gives 
rise  to  a  fine-meshed  network  of  capillaries  in  the  inner  layer  of  the 
theca.  From  the  capillaries  veins  arise  which  form  a  plexus  in  the 
medulla  and  leave  the  ovary  at  the  hilum. 

Lymphatics. — These  begin  as  small  lymph  spaces  in  the  cortex, 
which  communicate  with  more  definite  lymph  vessels  in  the  medulla, 
the  latter  leaving  the  organ  at  the  hilum. 

Nerves. — Medullated  and  non-medullated  fibres  enter  the  ovary 
at  the  hilum  and  follow  the  course  taken  by  the  blood-vessels.  Many 
of  the  fibres  end  in  the  vessel  walls;  others  form  plexuses  around  the 
follicle  and  end  in  the  theca  folliculi.  Some  describe  fibres  as  pass- 
ing through  the  theca  and  ending  in  the  follicular  epithelium.  Others 
claim  that  nerve  fibres  do  not  enter  the  follicle  proper.  Grou];)s  of 
sympathetic  ganglion  cells  occur  in  the  medulla  near  the  hilum. 

As  is  the  case  with  the  testicle,  certain  rudimentary  organs,  the 
remains  of  foetal  structures,  are  found  connected  with  the  ovary. 

The  poroophoron  consists  of  a  number  of  cords  or  tubules  of  epi- 
thelial cells,  sometimes  ciliated,  sometimes  non-ciliated.  It  is  found 
in  the  medulla,  or,  more  commonly,  in  the  connective  tissue  of  the 
hilum. 

The  cpoop/ioroii  is  a  similar  structure  found  in  the  folds  of  the 
broad  ligament.  Its  tuljulcs  open  into  a  duct  known  as  Gartner's 
duct.  In  man  this  duct  ends  Ijlindly.  In  some  of  the  lower  animals 
it   opens   into   the   \agina.     Both   paroophoron   and   epoophoron   are 


334  THE  ORGANS. 

remains  of  the  embryonal  mesonephros,  the  former  of  its  posterior 
segment,  the  latter  of  its  middle  segment. 

The  Oviduct. 

The  oviduct  or  Fallopian  tube  is  the  excretory  duct  of  the  ovary, 
serving  for  the  transmission  of  the  discharged  ovum  from  ovary  to 
uterus.  Although  there  is  no  sharp  demarcation  between  them,  it  is 
convenient  to  divide  the  tube  into  three  segments:  (i)  The  isthmus, 
beginning  at  the  uterus  and  extending  about  one-third  the  length  of 


^ 


f  A 


— d 


.^'^ 


Fig.  235. — Cross  Section  of  Oviduct  near  Uterine  End.  a,  Mucous  membrane;  h, 
circular  muscle  coat;  c,  longitudinal  muscle  coat;  d,  connective  tissue  of  serous  coat, 
(Orthmann.) 

the  tube;  (2)  the  ampulla,  about  twice  the  diameter  of  the  isthmus, 
and  occupying  somewhat  more  than  the  middle  third;  and  (3)  the 
fimbriated  or  ovarian  extremity. 

The  walls  of  the  oviduct  consist  of  three  coats:  (i)  Mucous,  (2) 
muscular,  and  (3)  serous  (Figs.  235  and  236). 

The  mucous  membrane  presents  numerous  longitudinal  foldings. 
In  the  embryo  four  of  these  folds  can  usually  be  distinguished,  and 
these  are  known  as  primary  folds.  In  the  adult  many  secondary 
folds  have  developed  upon  the  primary,  especially  in  the  ampulla  and 
fimbriated  extremity  where  the  folds  are  high  and  complicated  (Fig. 
236).  The  epithelium  lining  the  tube  is  of  the  simple  columnar 
cih'ated  type,  and  completely  covers  the  foldings  of  the  mucous  mem- 


THE  REPRODUCTIVE  SYSTEM.  335 

brane.  The  ciliary  motion  is  toward  the  uterus.  The  stroma  con- 
sists of  a  cellular  connective  tissue,  quite  compact  in  structure  in  the 
isthmus,  where  the  folds  are  low,  more  loosely  arranged  in  the  high 
folds  of  the  ampulla  and  fimbriated  extremity. 

The  muscular  coat  consists  of  an  inner  circular  and  an  outer  longi- 
tudinal layer.  The  latter  is  a  comparatively  thin  layer  in  the  isthmus, 
consists  of  discontinuous  groups  of  muscle  cells  in  the  ampulla,  and 
in  the  fimbriated  extremity  is  frequently  absent. 


>%^ 


v^^- 


Img.  236. — Cross  Section  of  Oviduct  near  Fimbriated  Extremity,  showing  complicated  fold- 
ings of  mucous  membrane.     (Orthmann.) 

The  serous  coat  has  the  usual  structure  of  peritoneum. 

The  larger  blood-vessels  run  in  the  stroma  along  the  bases  of  the 
folds.  They  send  off  branches  which  give  rise  to  a  dense  capillary 
network  in  the  stroma. 

Of  the  lymphatics  of  the  tube  little  is  known. 

The  nerves  form  a  rich  plexus  in  the  stroma,  from  which  branches 
pass  to  the  blood-vessels  and  muscular  tissue  of  the  walls  of  the  tube 
and  internally  as  far  as  the  epithehal  lining. 

TECHNIC. 

(i)  Child's  Ovary.— Remove  the  ovary  of  a  new-born  child,  being  careful  not 
to  touch  the  surface  epithelium,  fix  in  Zenker's  fluid  (technic  9,  p.  S),  and  harden 
in  alcohol.  Cut  sections  of  the  entire  organ  throtigh  the  hilum.  Stain  with 
htematoxylin-eosin  (technic  i,  p.  18)  and  mount  in  balsam. 

(2)  For  the  purpose  of  studying  the  Graatian  follicle  in  the  different  stages  of 


336 


THE  ORGANS. 


its  development  remove  an  ovary  from  an  adult  cat  or  dog  and  treat  as  above. 
Technic  (i).  These  sections  also,  as  a  rule,  are  satisfactory  for  the  study  of  the  cor- 
pus luteum. 

(3)  The  adult  human  ovary  is  little  used  for  histological  purposes  on  account 
of  the  few  follicles  it  usually  contains  and  its  proneness  to  pathological  changes. 
Its  study  is,  however,  so  extremely  important,  especially 
with  reference  to  the  pathology  of  the  ovary,  that  if  possible 
a  normal  human  ovary  should  be  obtained  from  a  young 
subject  for  purposes  of  comparison  with  the  above. 
Technic   (i). 

(4)  For  studying  the  egg  cords  of  Pfluger  and  their 
relation  to  the  germ  epithelium,  ovaries  of  the  human 
foetus,  and  of  very  young  cats,  dogs,  and  rabbits  are  satis- 
factory.    Technic  (i). 

(5)  Sections  of  the  fimbriated  end  of  the  oviduct  are 
usually  found  in  the  sections  of  ovary.  For  the  study  of 
other  parts  of  the  tube,  cut  out  thin  pieces  from  different 
regions,  fix  in  formalin-Miiller's  fluid,  stain  transverse  sec- 

[:.;d        tions  with  hfematoxylin-eosin,  and  mount  in  balsam. 

The  Uterus. 

The  wall  of  the  uterus  consists  of  three  coats 
which  from  without  inward  are  serous,  muscular, 
and  mucous. 

The  serous  coat  is  a  reflection  of  the  peritoneum, 
and  has  the  usual  structure  of  a  serous  membrane. 
The  muscularis  consists  of  bundles  of  smooth 
muscle  cells  separated  by  connective  tissue.  The 
muscle  has  a  general  arrangement  into  three  layers, 
an  inner,  a  middle,  and  an  outer,  which  are  distinct 
in  the  cervix,  but  not  well  defined  in  the  body  and 
fundus. 

The  inner  layer — stratum  submucosum — is  mainly 
Fig.      237.— Muscle    longitudinal,  although  some  obliquely  running  Ijun- 
dles  arc  usually  present. 

The  middle  layer — called  from  the  large  \'cnous 

channels  which  it  contains,  the  stratum  vasculare — 

is  the  thickest  of  the  three  layers,  forming  the  main 

bulk  of  the  muscular  wall.     It  consists  mainly  of  circularly  disposed 

muscle  bundles. 

The  outer  layer — stratum  supravasculare — is  thin  and  consists 
partly  of  circular  bundles,  partly  of  longitudinal.  The  latter  pre- 
dominate and  form  a  fairly  distinct  layer  just  beneath  the  serosa. 


b 


cells  from  (a)  non- 
jjregnant  uterus;  h, 
pregnant  uterus; 
drawn  to  same 
scale.     (Sellheim.) 


THE  REPRODUCTIVE  SYSTEM. 


337 


The  muscle  cells  of  the  uterus  are  long  spindle-shaped  elements, 
some  having  pointed,  others  blunt,  branched,  or  frayed  ends.  In  the 
\-irgin  uterus  they  have  a  length  of  from  40  to  60/1.  During  pregnancy 
the  muscular  tissue  of  the  uterus  is  greatly  increased.  This  is  due 
partly  to  increase  in  the  number,  partly  to  increase  in  the  size  of  the 
muscle  cells.  At  term  the  muscle  cells  frequently  ha\e  a  length  of 
from  250  to  600/i.      (Fig.  237.) 

The  mucous  membrane.  As  the  mucosa  presents  marked  \ariation 
in  structure,  dependent  upon  the  functional  condition  of  the  organ,  it  is 
necessary  to  describe: 


,.---  b 


1.  The  mucosa  of  the  resting 
uterus. 

2.  The  mucosa  of  the  men- 
struating uterus. 

3.  The  mucosa  of  the  preg- 
nant uterus. 


I.  The  Mucosa  of  the  Rest- 
ing Uterus. 

This  is  from  i  to  2  mm.  thick, 
and  consists  of  a  stroma,  glands, 
and  a  lining  epithelium  (Fig. 
238).  The  stroma  resembles 
embryonal  connective  tissue, 
consisting  of  fine  fibrils  and 
long,  irregular  branching  cells 
which  form  a  sort  of  network, 
the  meshes  of  which  are  filled  in 
with  lymphoid  cells  and  leuco- 
cytes. The  epithelium  is  of  the 
simple  high  columnar  ciliated 
variety,  the  ciliary  motion  being  toward  the  cervix.  A  basement 
membrane  separates  the  epithelium  from  the  underlying  stroma.  The 
glands  are  simple  forked  tubules  lined  by  a  single  layer  of  columnar 
ciliated  cells  resting  upon  a  basement  membrane  and  continuous  with 
the  surface  cells.  The  glands  extend  completely  through  the  stroma. 
Near  the  surface  they  run  a  comparatively  straight  course.  Deeper 
in  the  stroma  their  course  is  more  tortuous,  while  the  fundus  is  fre- 
quently turned  at  right  angles  to  the  rest  of  the  tulnile. 

In  the  cervix  the  stroma  is  firmer  and  less  cellular,  and  the  mu- 


FiG.  238. — From  Uterus  of  Young  \\'oman. 
(Bohm  and  von  Davidoff;  preparation  by 
Dr.  J.  Amann.)  X  34.  a,  Mucous  membrane: 
h,  surface  epithelium;  c,  gland;  r,  muscle. 


338  THE  ORGANS. 

cous  membrane  is  thicker  and  presents  numerous  folds — the  plicce 

palmatcE.     The  epithehum  is  higher  than  in  the  body  of  the  organ. 

In  addition  to  glands  like  those  found  in  the  body  of  the  uterus,  the 

cervical  mucosa  contains  peculiar  short,  sac-like  invaginations,  lined 

with  a  continuation  of  the  surface  epithelium,  which  secrete  a  glairy 

i  mucus.     Closure  of  the  mouths 

of  some  of  these  sacs  frequently 

r~  -.-^..trvjai-.'.J^S^  occurs,  leading  to  the  formation 

,/^;-  .  of  retention  cysts,  the  so-called 

~'\x    ,'^  ovula  Nabothi.     At  about  the 

a  .'- -  ._. .--    -  V ''t;  junction  of  middle  and  lower 

b ,'r . ->i      -  d     thirds  of  the  cervical  canal  a 


W^%^\  '         •  change  takes  place  in  the  epi- 


m 


thelium.        Here     the     simple 
.-  'iv  ,  -  "■         .-"■  *     columnar    ciliated    epithelium 

^'  -  "'       h     of     the     upper     part     of    the 

Fig.    23Q.-From    Section     of     Dog's    Cervix.  Cervix     gradually     pasSCS     OVer 

X4-     (Technic  2,  p.  34Q.)     a,  Cervical  canal;  into  a  Stratified  squamoUS  epi- 

b,   mucosa;   c,   folds  of  mucosa   (plicae  pal-  ,     ,. 

mate);  d,  muscle  layers  of  cervix;  e,  epithe-  thehum.      Near  the  external  OS 

Hum  of  vagina  and  vaginal  surface  of  cervix;  p^piH^      appear,      the      Vaginal 

./,  vagmal  epithehum;  g,  vagmal  mucosa;  li,  "    >-                 -rr        y                      o 

submucosa    and    muscularis    of    vagina;    /,  surface     of     the     cervix     being 

blood-vessels.  ,          .    ,                  ,      ,  •  r     i 

covered  with  a  stratified 
squamous  epithelium  with  underlying  papillae  similar  to  and  con- 
tinuous with  that  of  the  vagina. 

Near  the  external  os  the  epithelium  changes  over  into  the  strati- 
fied squamous  epithelium  with  underlying  papillae,  similar  to  that  of 
the  external  surface  of  the  cervix. 


2.  The  Mucosa  of  the  Menstruating  Uterus. 

This  consists  of  the  same  structural  elements  as  the  mucosa  of 
the  resting  uterus:  stroma,  glands,  and  lining  epithelium.  These, 
however,  undergo  certain  changes  which  may  be  conveniently  divided 
into  three  stages: 

(a)  The  stage  of  preparation. 

(b)  The  stage  of  menstruation  proper. 

(c)  The  stage  of  reparation. 

(a)  The  Stage  of  Preparation. — This  begins  se\eral  days 
before  the  actual  flow  of  blood,  and  is  marked  by  an  intense  hyper- 
a^mia  determining  a  swelling  and  growth  of  the  entire  mucosa.     The 


THE  REPRODUCTIVE  SYSTEM. 


339 


d     --^ 


It 


blood-vessels,  especially  the  capillaries  and  veins,  become  greatly 
distended,  thus  contributing  largely  to  the  increase  in  thickness  of 
the  mucosa.  There  are  also  proliferation  of  the  connective-tissue 
cells,  an  increase  in  the  number  of  leucocytes,  and  a  growth  of  the 
uterine  glands.  The  surface  at  the  same  time  becomes  irregular,  the 
glands  opening  into  deep  pits  or 
depressions,  and  the  glands  them- 
selves become  more  tortuous  and 
their  lumina  more  widely  open. 
The  mucous  membrane  has  now 
reached  a  thickness  of  about  6 
mm.,  and  is  known  as  the  de- 
cidua  menstriialis  (Fig.  240). 

{h)  The  Stage  of  ■  Men- 
struation Proper. — This  is 
marked  by  the  escape  of  blood 
from  the  engorged  vessels  and 
the  appearance  of  the  external 
phenomena  of  menstruation. 
The  blood  escapes  partly  by 
rupture  of  the  vessel  walls,  partly 
by  diapedesis.  The  hemorrhage 
is  at  first  subepithelial,  but  the 
epithelium  soon  gives  way  and 
the  blood  escapes  into  the  ca\'ity 
of  the  uterus.  Much  difference 
of  opinion  exists  as  to  the  amount 
of  epithelial  destruction  during 
menstruation,  some  claiming  that 
the  entire  epithelium  is  de- 
stroyed with  each  menstrual  period,  others  that  the  epithelium  remains 
almost  intact.  Complete  destruction  of  the  epithelium  is  hardly  com- 
patible with  the  restoration  of  the  epithelium  which  always  follows 
menstruation.  While  there  is  undoubtedly  destruction  of  most  or 
all  of  the  surface  epithelium  and  of  the  glands  to  some  considerable 
depth,  the  deeper  portions  of  the  glands  always  remain  to  take  part 
in   the  succeeding  regenerative  phenomena. 

(f)  The  Stage  of  Repartition. — After  from  three  to  five  days 
the  bleeding  from  ihe  uterine  mucosa  ceases  and  the  return  to  the 
resting  condition  begins.     This  is  marked  by  disappearance  of  the 


■  '■.•.■-p?*»o;,  ■■ . 


Fig.  240. — Section  through  Mucous  Alem- 
brane  of  Virgin  Uterus  during  First  Day  of 
Menstruation.  X  30.  (Schaper.)  a.  Sur- 
face epithelium;  h,  disintegrating  surface; 
c,  pit-like  depression  in  mucous  mem- 
brane; d,  excretory  duct;  e,  blood-vessels; 
g,  gland  tubule;  h,  dilated  gland  tubule; 
m,  muscularis. 


340  THE  ORGANS. 

congestion,  by  decrease  in  thickness  of  the  mucosa  and  in  the  size  of 
the  glands,  and  by  restoration  of  the  surface  epitheHum. 

3.  The  Mucosa  of  the  Pregnant  Uterus. 

This  is  known  as  the  decidua  graviditatis,  and  presents  changes 
in  structure  somewhat  similar  to  those  which  occur  during  menstrua- 
tion, but  more  extensive.     It  is  divided  into  three  parts: 

(a)  The  decidua  serotina  or  decidua  basalis-  that  part  of  the 
mucosa  to  which  the  ovum  is  attached. 

{h)  The  decidua  reflexa  or  decidua  capsularis — that  part  of  the 
mucosa  which  surrounds  the  ovum. 

(r)   The  decidua  vera — which  consist  of  all  the  remaining  mucosa. 

The  development  of  the  decidua  vera  resembles  the  changes  which 
take  place  in  the  mucosa  during  menstruation.  There  is  the  same 
thickening  of  the  mucosa,  and  this  thickening  is  due  to  the  same 
factor,  i.e.,  distention  of  the  blood-vessels  and  proliferation  of  the 
tissue  elements.  These  changes  are,  however,  much  more  extensive 
than  during  menstruation.  The  superficial  part  of  the  stroma  be- 
tween the  mouths  of  the  glands  becomes  quite  dense  and  firm,  form- 
ing the  compact  layer.  The  deeper  part  of  the  stroma  contains  nu- 
merous cavities,  which  are  the  lumina  of  the  now  widely  distended 
and  tortuous  glands.     This  is  known  as  the  spongy  layer. 

Within  the  stroma,  especially  of  the  compact  layer,  develop  the  so- 
called  decidual  cells.  These  are  peculiar  typical  cells  derived  from  con- 
nective tissue.  They  are  of  large  size  (30  to  ioo/(),  vary  greatly  in 
shape,  and  in  the  later  months  of  pregnancy  have  a  rather  characteristic 
brown  color,  which  they  impart  to  the  superficial  layers  of  the  decidua 
vera.  They  are  mostly  mononuclear,  although  polynuclear  forms  occur. 

Luring  the  latter  half  of  pregnancy  there  is  a  gradual  thinning 
of  the  decidua  vera,  due  apparently  to  pressure.  The  necks  of  the 
glands  in  the  compact  layer  disappear,  and  the  gland  lumina  in  the 
spongy  layer  are  changed  into  elongated  spaces,  which  lie  parallel  to 
the  muscular  layer. 

The  decidua  reflexa  and  decidua  serotina  have  at  first  the  same 
structure  as  the  decidua  \'era.  The  decidua  reflexa  undergoes  hyaline 
degeneration  during  the  early  part  of  pregnancy,  and  by  the  end  of 
gestation  has  either  completely  disappeared  (Minot)  or  has  fused  with 
the  decidua  vera  (Leopold). 

The  decidua  serotina  undergoes  changes  connected  with  the 
develojjment  of  the  placenta. 


THE  REPRODUCTIVE  SYSTEM.  341 


The  Placenta/ 


The  placenta  consists  of  two  parts,  one  of  which  is  of  maternal 
origin — placenta  uterina — the  other  of  foetal  origin — the  placenta  foe  talis. 
As  it  is  in  the  placenta  that  the  interchange  takes  place  between  the 
maternal  and  the  foetal  blood,  the  relations  between  the  maternal  and 
foetal  parts  of  the  placenta  are  extremely  intimate.  This  relation 
consists  essentially  in  the  growing  out  from  the  foetal  placenta  of 
linger-like  projections — villi — which  penetrate  the  maternal  placenta, 
the  latter  being  especially  modified  for  their  reception. 

The  Placenta  Fcetalis. — This  is  a  differentiated  portion  of  the 
chorion.  On  the  surface  directed  toward  the  foetus  the  chorion  after 
the  third  month  is  covered  by  a  delicate  foetal  membrane,  the  placental 
portion  of  the  amnion.  This  consists  of  a  surface  epithelium,  resting 
upon  a  layer  of  embryonal  connective  tissue  which  attaches  it  to  the 
chorion.  The  chorion  consists  of  {a)  a  compact  layer — the  membrana 
chorii — composed  at  first  of  embryonal,  later  of  fibrous,  connective 
tissue,  and  containing  the  main  branches  of  the  umbilical  vessels  and 
{b)  an  inner  ^•illous  layer,  which  gives  rise  to  finger-like  projections 
which  extend  down  from  the  the  foetal  into  the  maternal  placenta  and 
serve  to  connect  the  two. 

The  chorionic  villi  first  appear  as  short  projections  composed 
entirely  of  epithelium.  Each  of  these  primary  villi  branches  dichoto- 
mously,  giving  rise  to  a  number  of  secondary  villi.  As  they  develop, 
the  central  portion  of  the  original  solid  epithelial  structure  is  replaced 
by  connective  tissue.  Septa  of  connective  tissue  from  the  maternal 
placenta  pass  down  among  the  villi  and  separate  them  into  groups  or 
cotyledons.  The  main  or  primary  villi  run  a  quite  straight  course  from 
the  chorion  into  the  maternal  placental  tissue,  apparently  serving  to 
secure  firm  union  between  the  two.  They  are  thus  known  as  roots  of 
attachment  or  fastening  villi  (Fig.  241).  The  secondary  villi  are  given 
off  laterally  from  the  primary  villi,  end  freely  in  the  spaces  between 
the  latter — intervillous  spaces  (Fig.  241) — and  are  known  as  free,  ter- 
minal or  floating  villi  (Fig.  241). 

The  chorionic  villus  thus  consists  of  a  central  core  of  connective 
tissue  covered  by  a  layer  of  epithelium.  The  connective  tissue  is  of  the 
mucous  type  and  serves  for  the  transmission  of  numerous  blood- 
vessels.    In  the  \"illi  of  early  pregnancy  the  epithelium  consists  of  an 

'■  For  many  facts  as  to  the  structure  of  the  placenta,  the  writer  is  indebted  to  the 
excellent  chapter  on  the  subject  added  by  Prof.  .Alfred  Schaper  to  the  tifth  edition  of 

Stohr's  "Textbook  of  Histolosv." 


342 


THE  ORGANS. 


THE  REPRODUCTR'E  SYSTEM. 


343 


inner  layer  of  distinctly  outlined  cells  and  an  outer  layer  of  fused  cell 
bodies — a  syncytium  (Fig,  243,  A,  a) — containing  small  scattered  nuclei. 
The  villi  of  the  later  months  of  pregnancy  have  no  definite  epithelial 
covering,  but  are  surrounded  by  a  delicate  hom.ogeneous  membrane, 
probably  the  remains  of  the  syncytium.  At  various  points  on  the 
surface  of  the  villus  are  groups  of  nuclei.  These  stain  intensely,  are 
surrounded  Ijy  a  homogeneous  protoplasm,  and  form  knob-like  pro- 
jections above  the  general  surface  of  the  villus.     They  are  known  as 


"Giant"    cell 


Syncytium 


Trophodi 
mass 


Fig.  242. — Section  of  Chorion  of  Human  Embryo  of  one  month  (9  mm.).      (Grosser.) 

cell  patches,  or  more  properly  as  nuclear  groups  (Fig.  243,  f),  and  repre- 
sent remains  of  the  nuclei  of  the  ejjithelium  of  the  younger  villus. 
Between  the  nuclear  groups  the  \"illus  is  covered  only  by  a  thin  homo- 
geneous membrane.  Small  villi  usually  resemble  more  closelv  in 
structure  the  younger  villus,  being  frequently  covered  by  a  nucleated 
syncytium.  Portions  of  the  syncytium,  especially  of  older  villi,  some- 
times become  changed  into  a  peculiar  hyaline  substance  containing 
numerous  channels.  This  is  known  as  canalized  fibrin,  and  mav  form 
dense  layers  ui)on  the  surface  of  the  chorion.     (Fig.  242.) 

The  Placenta  Uterixa. — This  de^■elops  from  the  decidua  sero- 
tina.     The  latter  becomes  much  thinner  than  the  rest  of  the  decidua 


344 


THE  ORGANS. 


(decidua  vera),  but  still  shows  a  division  into  a  deeper  spongy  portion 
containing  gland  tubules,  and  a  superficial  compact  portion  in  which 
are  large  numbers  of  decidual  cells.  From  the  superficial  portion 
connective-tissue  septa — placental  septa — grow  into  the  foetal  placenta, 
as  described  above,  separating  its  villi  into  cotyledons.  Near  the 
margins  of  the  placenta  these  septa  pass  to  the  chorionic  membrane 

and  form  beneath  it  a  thin  mem- 
brane, the  subchorionic  placental 
decidua.  At  the  edge  of  the  pla- 
centa, where  decidua  serotina  passes 
over  into  the  thicker  decidua  vera, 
there  is  a  close  attachment  of  the 
chorion  to  the  former. 

As  the  placenta  serves  as  the 
place  of  interchange  of  materials 
between  the  maternal  and  the  foetal 
circulations,  the  arrangement  of  the 
placental  blood-vessels  is  of  especial 
importance.  Arterial  branches  from 
vessels  of  the  uterine  muscularis 
enter  the  serotina.  In  the  very 
tortuous  course  which  these  vessels 
take  through  the  serotina  (Fig.  241) 
their  walls  lose  their  muscular  and 
connective-tissue  elements  and  be- 
come reduced  to  epithelial  tubes.  These  branch  in  the  placental 
septa  and  finally  open  into  the  intervillous  spaces  along  the  edges 
of  the  cotyledons.  The  veins  take  origin  from  these  spaces  near 
the  centres  of  the  cotyledons.  The  maternal  blood  thus  passes 
through  the  intervillous  spaces  from  periphery  to  centre,  and  in  its 
course  comes  into  direct  contact  with  the  freely  terminating  chorionic 
villi.  Jt  is  to  be  noted  that  the  Ijlood-vessel  systems  of  the  mother 
and  of  the  f(x,-tus  are  both  closed  systems,  and  that  consequently  there 
is  no  direct  admixture  of  maternal  and  fcEtal  blood.  Interchange  of 
materials  must  therefore  always  take  place  through  the  capillary  walls 
and  through  the  walls  of  the  chorionic  villi.     (Fig.  241.) 

Blood-vessels. — The  arteries  enter  the  uterus  from  the  broad  hga- 
ment  and  j;ass  to  the  stratum  vasculare  of  the  muscularis,  where  they 
undergo  extensive  ramification.  From  the  arteries  of  the  stratum 
vasculare  branches  pass  to  the  mucosa  and  give  rise  to  capillary  net- 


FlG.      2 


43-- 


Cross  Sections  of  Human 
Chorionic  Villi  at  End  of  Pregnancy. 
X  250.  (Schaper.)  A,  Small  villus; 
B,  larger  villus,  a,  Protoplasmic  coat 
(syncytium);  h,  epithelial  nucleus;  c, 
nuclear  groups;  d,  small  artery;  e,  small 
vein;/,  capillaries. 


THE    REPROULXTIX'E   SVSTE.\L  345 

works,  which  surround  the  glands  and  are  especially  dense  just  beneath 
the  surface  epithelium.  From  these  capillaries  the  blood  passes  into  a 
plexus  of  veins  in  the  deeper  portion  of  the  mucosa,  and  these  in  turn 
empty  into  the  venous  plexuses  of  the  stratum  vasculare.  Thence  the 
veins  accompany  the  arteries,  leaving  the  uterus  through  the  broad 
ligament. 

Lymphatics. — These  begin  as  minute  spaces  in  the  stroma  and 
empty  into  the  more  definite  lymph  channels  of  the  muscularis,  which 
are  especially  well  developed  in  the  stratum  vasculare.  These  in  turn 
communicate  with  the  larger  lymph  vessels  in  the  subserous  connective 
tissue. 

Nerves. — Both  medullated  and  non-medullated  nerve  fibres  occur 
in  the  uterus.  The  latter  are  associated  with  minute  sympathetic 
ganglia  and  supply  the  muscular  tissue.  The  medullated  fibres  form 
plexuses  in  the  mucosa,  from  which  are  given  off  fine  fibres  which 
terminate  freely  between  the  cells  of  the  surface  epithelium  and  of  the 
uterine  glands. 

The  Vagina. 

The  wall  of  the  vagina  consists  of  four  coats,  which  from  without 
inward  are  fibrous,  muscular,  sulDmucous,  and  mucous. 

The  fibrous  coat  consists  of  dense  connective  tissue  with  many 
coarse  elastic  fibres.  It  serves  to  connect  the  vagina  with  the  sur- 
rounding structures. 

The  muscular  coat  is  indistinctly  divided  into  an  outer  longitudinal 
and  an  inner  circular  layer.  The  latter  is  usually  not  well  developed 
and  may  be  absent. 

The  suhmucosa  is  a  layer  of  loose  connective  tissue,  especially  rich 
in  elastic  fibres  and  blood-vessels.  Numerous  large  venous  channels 
give  to  the  submucosa  the  character  of  erectile  tissue. 

The  mucous  membrane  consists  of  a  papillated  connective-tissue 
stroma  of  mixed  fibrous  and  elastic  tissue.  The  stroma  usually  con- 
tains dift'use  lymphoid  tissue  and  more  rarely  solitary  nodules.  Cover- 
ing the  stroma  is  a  stratified  squamous  epithelium,  the  surface  cells  of 
which  are  extremely  thin.  The  surface  of  the  mucosa  is  not  smooth, 
but  is  folded  transversely,  forming  the  so-called  rugcr.  Most  authorities 
agree  that  glands  are  wanting  in  the  vagina,  the  mucus  found  there 
being  derived  from  the  glands  of  the  cervix. 

Blood-vessels. — The  larger  Ijlood-vcssels  run  in  the  sul)mucosa, 
giving;  oft"  l^ranchcs  which  break  ui)  into  cainllarv  networks  in  the  sub- 


34:6  THE  ORGANS. 

mucosa,  muscularis,  and  stroma.  The  vascular  networks  have  a 
general  direction  parallel  to  the  surface.  The  capillaries  empty  into 
veins  which  form  a  plexus  of  broad  venous  channels  in  the  muscularis. 

The  Lymphatics. — These  follow  in  general  the  distribution  of 
the  blood-vessels. 

Nerves. — Nerve  fibres  from  both  cerebro-spinal  and  sympathetic 
systems  are  found  in  the  vagina.  Medullated  (sensory)  fibres,  the 
dendrites  of  spinal  ganglion  cells,  form  plexuses  in  the  mucosa,  from 
which  are  given  off  delicate  non-medullated  terminals  to  the  epithelial 
cells.  Non-medullated  sympathetic  fibres  supply  the  muscularis 
and  the  muscle  of  the  vessel  walls.  Along  these  nerves  are  small 
sympathetic  ganglia. 

In  the  vestibule  the  epithelium  gradually  takes  on  the  structure  of 
epidermis.  Here  are  located  small  mucous  glands — glandiilcE  vestih- 
ulares  minores — especially  numerous  around  the  clitoris  and  opening 
of  the  urethra.  Larger  mucous  glands — glandula  vestibulares  majores, 
or  glands  of  Bartholin — analogous  to  Cowper's  glands  in  the  male,  are 
also  found  in  the  walls  of  the  vestibule. 

The  clitoris  consists  mainly  of  erectile  tissue  similar  to  that  of  the 
corpora  cavernosa  of  the  penis.  It  is  covered  with  a  thin  epithelium 
with  underlying  papillas,  and  is  richly  supplied  w^th  nerves  having 
highly  specialized  terminations. 

Development  of  the  Urinary  and  Reproductive  Systems. 

The  development  of  the  genito-urinary  system  is  com.plicated  by  the 
appearance,  and  disappearance  for  the  most  part,  of  two  sets  of  urinary 
organs,  and  the  final  formation  of  the  permanent  set.  The  three 
sets,  in  the  order  of  their  appearance,  are  the  pronephroi,  mesonephroi, 
and  metanephroi.  The  first  two  sets,  which  are  ])resent  only  in  the 
embryo  in  the  higher  animals,  are  the  representatives  of  organs  that 
function  in  the  adult  in  the  lower  vertebrates.  They  are  also  inti- 
mately concerned  in  the  development  of  the  efferent  duct  system  of  the 
male  reproductive  organs  in  higher  animals.  The  metanephroi, 
generally  known  as  the  kidneys,  are  the  functional  urinary  organs  in 
the  majority  of  re];tiles  and  in  all  birds  and  mammals. 

The  pronephroi  are  represented  in  the  human  embryo  of  3  to  5  mm. 
by  one  fjr  two  small,  condensed  masses  of  mesoderm  just  lateral  to 
the  primitive  segments  on  each  side  in  the  cervical  region.  These 
masses,  which  are  probably  derived  from  the  mesothelial  lining  of  the 


THE    REPRODUCTIVE    SYSTEM.  347 

body  cavity,  may  or  may  not  become  hollow,  but  do  not  connect  with 
the  pronephric  duct,  and  soon  disappear.  The  pronephric  duct 
appears  about  the  same  time  as  a  derivative  of  the  mesoderm  just 
lateral  to  the  primitive  segments.  It  extends  from  the  cervical  region 
to  the  caudal  region  of  the  embryo  where  it  bends  mesially  and 
opens  into  the  gut.  These  ducts  persist  and  become  the  ducts  of  the 
mesonephroi. 

The  mesonephroi  begin  to  develop  almost  as  soon  as  the  proneph- 
roi  and  just  caudal  to  them.  Condensations  appear  in  the  mesodermal 
tissue  lateral  to  the  primitive  segments  and  become  more  or  less  tor- 
tuous. Lamina  appear  in  these  condensations,  thus  forming  tubules 
which  then  connect  at  one  end  with  the  pronephric  duct  (now  the 
mesonephric  or  Wolffian  duct).  The  tubules  develop  progressively 
from  before  backward  and  finally  form  a  series  extending  from  the 
cervical  region  to  the  pelvic  region  of  the  embryo.  At  the  distal  end 
of  each  tubule  a  glomerulus,  containing  branches  from  the  aorta, 
develops.  The  tubules  increase  in  length  and  number  and  come  to 
form  a  pair  of  large  structures  which  project  into  the  dorsal  part  of  the 
body  cavity.  These  are  often  spoken  of  as  the  Wolffian  bodies.  They 
reach  the  height  of  their  development  during  the  fifth  or  sixth  week. 

During  the  period  of  their  existence  in  the  embryo  in  higher  animals, 
the  mesonephroi  functionate  as  urinary  organs,  not  only  through  the 
agency  of  the  glom.eruli  but  also  by  means  of  the  epithelium  of  the 
tubules  themselves,  among  which  numerous  branches  of  the  posterior 
cardinal  veins  ramify. 

From  the  sixth  week  on,  and  coincident  with  the  development  of 
the  metanephroi  or  kidneys,  the  mesonephroi  atrophy,  leaving  finally 
only  certain  parts  which  differ  in  the  two  sexes.  In  the  male  some 
of  the  tubules  in  the  cephalic  portion  persist  as  the  vasa  eft'erentia, 
while  a  few  in  the  caudal  portion  remain  as  the  paradidymis  and  vasa 
aberrantia;  the  duct  persists  as  the  vas  epididym.idis,  vas  deferens, 
and  ejaculatory  duct.  In  the  female  the  mesonephric  tubules  dis- 
appear for  the  most  part,  only  a  few  remaining  to  form  the  epo- 
ophoron  and  paroophoron,  while  the  duct  persists  in  part  as  Gartner's 
canal. 

Each  kidney  begins  in  embryos  of  5  to  6  mm.  as  a  hollow  bud  on 
the  dorsal  side  of  each  mesonephric  duct  near  its  opening  into  the  gut. 
This  bud  grows  dorsally,  and  then  turns  cranially  in  the  mesoderm 
between  the  vertebral  column  and  ihc  mesonei)hros.  The  prtiximal 
portion  remains  more  slender  as  the  ureter,  white  the  di>tal  end  hu- 


348  THE  ORGANS. 

comes  dilated  to  form  the  primitive  renal  pelvis.  From  this  dilated  end 
a  number  of  secondary  evaginations  grow  out  to  form  the  papillary 
ducts  and  straight  collecting  tubules. 

The  mesodermal  tissue  surrounding  the  outgrowths  from  the 
primitive  renal  pelvis  becomes  condensed  in  places  and  gives  rise  to 
the  convoluted  portions  of  the  uriniferous  tubules  and  to  Henle's  loops. 
A  glomerulus  develops  in  connection  with  the  distal  end  of  each  con- 
voluted tubule.  The  portion  of  each  tubule  derived  from  the  meso- 
dermal tissue  unites  secondarily  at  the  arched  (junctional)  tubule 
with  the  portion  derived  from  the  renal  pelvis.  Thus  the  kidney 
tubules  are  derived  in  part  directly  from  undifferentiated  mesoderm 
(convoluted  tubules  and  Henle's  loops)  and  in  part  from  an  outgrowth 
from  the  mesonephric  duct  (straight  collecting  tubules  and  papillary 
ducts) . 

During  foetal  life  the  kidneys  are  distinctly  lobulated,  but  after 
birth  the  surface  becomes  quite  smooth. 

The  genital  gland  on  each  side  appears  on  the  mesial  surface  of 
the  mesonephros  as  a  thickening  of  a  narrow  band  of  the  mesothelial 
lining  of  the  body  cavity.  The  cells  in  the  band  become  differentiated 
into  two  kinds — small  cuboidal  cells  which  stain  rather  intensely,  and 
larger  spherical  cells  with  clearer  cytoplasm  and  vesicular  nuclei. 
The  latter  are  the  sex  cells  which  are  destined  to  give  rise  to  the  ova 
in  the  female  or  the  spermatozoa  in  the  male.  The  whole  thickened 
band  is  known  as  the  germinal  epithelium. 

The  cells  of  the  germinal  epithelium  increase  in  number  by  mitosis 
and  soon  become  differentiated  into  two  layers — a  superficial  layer 
which  retains  its  epithelial  character  and  contains  the  sex  cells,  and  a 
dee]jer  layer  which  is  destined  to  give  rise  in  part  to  the  stroma  of  the 
genital  gland.  The  elevation  caused  by  the  increased  number  of  cells 
projects  into  the  body  cavity  as  the  genital  ridge.  From  the  superfi- 
cial layer  containing  the  sex  cells  a  number  of  plugs  or  columns  of  cells 
grow  down  into  the  deeper  layer  carrying  some  of  the  sex  cells  with 
them.  Thus  far  (up  to  about  the  fifth  week)  the  changes  are  common 
to  both  sexes,  and  only  later  does  the  sex  differentiation  occur. 

After  aljout  the  fifth  week  certain  changes  occur  in  the  genital 
ridge  which  differ  accordingly  as  the  ridge  is  to  become  an  ovary  or  a 
testicle.  In  the  case  of  the  ovary  a  layer  of  loose  connective  tissue 
grows  in  between  the  surface  epithelium  and  the  cell  columns  or  plugs 
mentioned  above.  The  cell  columns  are  thus  pushed  farther  from  the 
surface  and  constitute  the  medullary  cords.     These  ultimately  disap- 


THE    REPRODUCTIVE    SYSTEM.  349 

pear.  The  surface  epithelium  again  sends  plugs  of  cells  (Pfliiger's 
egg  cords)  down  into  the  underlying  tissue.  These  cords  are  made  up 
for  the  most  part  of  epithelial  cells  which  give  rise  to  the  follicular  cells, 
but  contain  also  a  considerable  number  of  sex  cells  (primitive  ova). 
The  egg  cords  then  become  broken  up  into  smaller  masses  each  of 
which  contains  a  single  primitive  ovum  (rarely  more)  and  constitutes 
a  primitive  Graafian  follicle.  The  sex  cell  grows  in  size  and  becomes 
the  primary  occyte  (and  finally  the  mature  ovum),  while  the  epithelial 
cells  around  it  give  rise  to  the  stratum  granulosum  and  germ  hill  of 
the  mature  Graafian  follicle.  During  these  processes  the  stroma 
also  increases  in  amount,  while  the  original  germinal  epithelium 
becomes  reduced  to  a  single  layer  of  cuboidal  cells.  The  formation 
of  egg  cords  is  usually  completed  before  birth.     (See  also  p.  324.) 

In  the  case  of  the  testicle  a  layer  of  dense  connective  tissue,  the 
tunica  albuginea,  develops  between  the  germinal  epithelium  and  the 
sex  cords.  The  epithelium  becomes  reduced  to  a  single  layer  of  fiat 
cells.  The  sex  cords  which  first  grew  into  the  underlying  tissue  and 
which  contain  the  sex  cells,  are  destined  to  give  rise  to  the  con^•oluted 
seminiferous  tubules.  This  phase  of  development  dift'ers  from  that 
in  the  ovary  inasmuch  as  in  the  latter  case  the  first  formed  sex  cords 
(medullary  cords)  disappear,  Pfliiger's  egg  cords  being  formed  later 
and  having  no  homologue  in  the  testicle.  The  sex  cords  of  the  testicle 
become  more  and  more  convoluted  and  the  sex  cells  (spermatogonia) 
proliferate  rapidly.  Beginning  after  birth  and  continuing  up  to  the 
time  of  puberty,  lumina  appear  in  the  sex  cords  and  they  thus  give  rise 
to  the  convoluted  seminiferous  tubules.  The  supporting  cells  (of 
Sertoli)  are  probably  derived  from  the  undifferentiated  epithelial 
cells  of  the  sex  cords.      (See  also  p.  305.) 

TECHNIC. 

(i)  A  human  uterus — if  possible  from  a  young  adult — or,  if  this  cannot  be  ob- 
tained, the  uterus  of  a  cat  or  dog,  is  cut  transversely  into  slices  about  i  cm.  thick 
and  fixed  in  Zenker's  fluid  (technic  9,  p.  8)  or  in  formalin-Miiller's  fluid  (technic 
5,  p.  7).  For  topography  these  slices  are  cut  in  half  through  the  middle  of  the 
uterine  cavity  and  sections  made  through  the  entire  half  organ.  These  are  stained 
with  haematoxylin-picro-acid-fuchsin  (technic  3,  p.  iq)  and  mounted  in  balsam. 
For  details  of  the  mucous  membrane,  cut  away  most  of  the  muscle  from  around  the 
half  slice,  being  careful  not  to  touch  the  mucous  surface;  make  thin  sections,  stain 
with  hasmatoxylin-eosin  (technic  i,  p.  18),  and  mount  in  balsam. 

(2)  Sections  of  the  cervix  may  be  prepared  in  the  same  manner  as  the  preceding. 

(3)  Placental  tissue  may  be  cut  into  small  cubes  and  treated  with  tlie  same 
technic  (i). 


350  THE  ORGANS. 

(4)  If  a  human  or  animal  uterus  with  the  placenta  in  situ  is  obtainable  it  should 
be  cut  into  thin  slices  and  fixed  in  formalin-Miiller's  fluid.  The  blocks  of  tissue 
should  be  so  arranged  that  sections  include  the  utero-placental  junction.  They 
may  be  stained  with  haematoxylin-eosin  or  with  haematoxylin-picro-acid-fuch- 
sin  (see  above). 

(5)  Treat  pieces  of  the  human  vagina  according  to  technic  i,  p.  223. 

General  References  for  Further  Study. 

Ballowitz:  Weitere  Beobachtungen  iiber  den  feineren  Bau  der  Saugethier- 
Spermatozoen.     Zeit.  f.  wiss.  Zool.,  Bd.  Hi.,  1891. 

Hertwig:  Lehrbuch  der  Entwickelungsgeschichte  des  Menschen  und  der  Wir- 
belthiere,  Jena,  1896. 

Kolliker:  Handbuch  der  Gewebelehre  des  Menschen. 

Nagel:  Das  menschliche  Ei.     Arch.  mik.  Anat.,  Bd.  xxxi.,  1888. 

Ruckert:  Zur  Eireifung  der  Copepoden.     Anat.  Hefte,  I.  Abth.,  Bd.  iv.,  1894. 

Schaper:  Chapter  on  the  Placenta  in  Stohr's  Text-book  of  Histology,  5th  ed. 

Sobotta:  Ueber  die  Bildung  des  Corpus  luteum  bei  der  Maus.  Arch.  f.  mik. 
Anat.,  Bd.  xlvii.,  1896. — Ueber  die  Bildung  des  Corpus  luteum  beim  Kaninchen. 
Anat.  Hefte,  I.  Abth.,  Bd.  viii.,  1897. 


CHAPTER  X. 
THE  SKIN  AND  ITS  APPENDAGES. 

The  Skin. 

The  skin  or  cutis  consists  of  two  parts:  (i)  The  derma,  corium, 
or  true  skin,  and  covering  this,  (2)  the  epidermis  or  cuticle.  The 
derma  is  a  connective-tissue  derivative  of  the  mesoderm,  the  epider- 
mis an  epithelial  derivative  of  the  ectoderm. 

The  Derma. — This  is  divided  into  two  layers  which  blend  with- 


Fig.  244. — Vertical  Section  of  Thin  Skin,  Human.  X  60.  (Technic  2,  p.  356.)  a. 
Epidermis;  b,  pars  papillaris  of  derma;  c,  papilla:;  d,  pars  reticularis  of  derma;  e,  duct  of 
sweat  gland;/,  sweat  gland;  g,  subcutaneous  fat. 

out  distinct  demarcation.     The  deeper  is  known  as  the  pars  reticu- 
laris, the  more  superficial  as  the  pars  papillaris  (Fig.  244). 

The  pars  reticularis  is  made  up  of  rather  coarse,  loosely  arranged 


352 


THE  ORGANS. 


white  and  elastic  tibres  with  connective-tissue  cells  in  varying  num- 
bers. The  fibres  run  for  the  most  part  parallel  to  the  surface  of  the 
skin. 

The  pars  papillaris  is  similar  in  structure  to  the  preceding,  but 
both  white  and  elastic  fibres  are  finer  and  more  closely  arranged. 
Externally  this  layer  is  marked  by  minute  folds  which  are  visible  to 
the  naked  eye,  and  can  be  seen  intersecting  one  another  and  enclos- 
ing small  irregular  areas  of  skin.  In  the  thick  skin  of  the  palms  and 
soles  these  furrows  are  close  together  and  parallel,  while  between 
them  are  long  corresponding  ridges.     In  addition  to  the  furrows  and 


A 


B\ 


C 


Fig.  245. — Thick  Vertical  Section  through  Skin  of  Finger  Tip.  (Merkel-Henle.)  A, 
Epidermis;  B,  derma;  C,  subcutis.  a,  Stratum  corneum;  b,  duct  of  sweat  gland;  c,  stratum 
lucidum;  d,  stratum  germinativum;  e,  papilla  of  derma;/,  derma;  g,  blood-vessel;  h,  sweat 
gland;  i,  fat  lobule;  p,  sweat  pore. 

ridges  the  entire  surface  of  the  corium  is  beset  with  minute  papillae. 
These  vary  in  structure,  some  ending  in  a  single  point — simple  pa- 
pillce — others  in  several  y^oints — compound  papilla';  some  containing 
blood-vessels — vascular  papilla';  others  containing  special  nerve 
terminations — nerve  papilla'.  (Fig.  246). 

Smooth  muscle  cells  occur  in  the  corium  in  connection  with  the 
sweat  glands.  In  the  skin  of  the  scrotum^ — -tunica  dartos — and  of  the 
nipple,  the  smooth  muscle  cells  are  arranged  in  a  network  parallel  to 
the  surface.  In  the  face  and  neck  striated  muscle  fibres  j^enctrate  the 
corium. 

Beneath  the  corium  is  the  siibculaneous  tissue.     This  consists  of 


THE  SKIN  AND  ITS  APPENDAGES. 


353 


vertically  disposed  bands  of  connective  tissue — the  retinaculce  cutis — 
which  serve  to  unite  the  corium  to  the  underlying  structures  and 
enclose  fat  lobules.  In  some  parts  of  the  body  this  subcutaneous  fat 
forms  a  thick  layer — the  panniculus  adiposus. 

The  Epidermis. — This  is  composed  of  stratified  squamous  epi- 
thelium. In  the  comparatively  thin  skin  of  the  general  body  surface 
the  epidermis  is  divided  into  two  sub-layers:  (i)  One  lying  just  above 
the  papillary  layer  of  the  derma,  and  known  as  the  stratum  germina- 


FiG.  246. — From  Vertical  Section  through  Skin  of  Human  Finger  Tip.  X  2co. 
(Schafer.)  a.  Stratum  corneum;  b,  stratum  lucidum;  c,  stratum  granulosum;  d,  stratum 
germinativum.  To  the  left  a  vascidar  papilla;  to  the  right  a  nerve  papilla  containing  tactile 
corpuscle. 


tivum  (stratum  mucosum — stratum  Malpighii);  (2)  the  other  con- 
stituting the  superficial  layer  of  the  skin — the  horny  layer  or  stratum 
corneum.  In  the  thick  skin  of  the  palms  and  soles  two  additional 
layers  are  developed;  (3)  the  stratum  granulosum;  and  (4)  the  stratum 
lucidum  (Fig.  245). 

(i)  The  stratum  gcnninaliviDJi  consists  of  several  layers  of  cells. 
The  deepest  cells  arc  columnar  and  form  a  single  layer  (stratum 
cylindricum),  which  rests  u]jon  a  basement  membrane  separating  it 


354 


THE  ORGANS. 


® 


(^' 


■Q 


t 


«tD 


from  the  derma.  The  membrane  and  cells  follow  the  elevations  and 
depressions  caused  by  the  papillae.  The  rest  of  the  stratum  germi- 
nativum  consists  of  large  polygonal  cells.  These  cells  have  well- 
developed  intercellular  bridges,  which 
appear  as  spines  projecting  from 
the  surfaces  of  the  cells.  For  this 
reason  the  cells  are  sometimes  called 
"prickle"  cells,  and  the  layer,  the 
"stratum  spinosum."  The  spines 
cross  minute  spaces  between  the  cells, 
which  are  believed  to  communicate 
with  the  lymph  spaces  of  the  derma 
(Fig.  247,  c).  The  cells  of  the  stratum 
germinativum  are  usually  in  a  state 
of  active  mitosis. 

(2)  The  stratum  granulosum  is  well 
developed  only  where  the  skin  is  thick. 
It  consists  of  from  one  to  three  layers 
of  flattened  polygonal  cells.  The 
protoplasm  of  these  cells  contains 
deeply  staining  granules — keratohya- 
line  granules — which  probably  repre- 
sent a  stage  in  the  formation  of  the 
horny  substance — keratin — of  the 
corneum  cells.  The  nuclei  of  these 
cells  always  show  degenerative 
changes,  and  there  is  reason  for  be- 
lieving that  this  karyolysis  is  closely 
associated  with  the  formation  of  the 
keratohyaline  granules  (Fig.  247,  h). 

(3)  The  stratum  hicidmn  is  also 
best  developed  where  the  skin  is 
thickest.  It  consists  of  two  or  three 
layers  of  flat  clear  cells,  the  outlines  of 
which  are  frequently  so  indistinct  that 

the  layer  appears  homogeneous.  The  transparency  of  the  cells  is  due 
to  the  presence  of  a  substance  known  as  eleidin,  and  derived  from 
the  keratohyaline  granules  of  the  stratum  granulosum  (Fig.  247,  a). 

(4)  The  stratum  corneum  varies  greatly  in  thickness,  reaching  its 
greatest  development  in  the  skin  of  the  palms  and  soles.     The  cells 


^ 


( 


^j 


t 


wf; 


t\^ 


W'V 


Fig.  247. — From  Vertical  Section 
through  Thick  Skin.  (Mcrkel- 
Henle.)  a,  Stratum  lucidum;  /;, 
stratum  granulosum;  c,  stratum 
germinativum,  showing  intercel- 
lular briflges. 


THE  SKIN  AND  ITS  APPENDAGES.  355 

are  flattened  and  horny,  especially  near  the  surface.  Some  appear 
homogeneous,  others  have  a  lamellated  appearance.  They  contain 
pareleidin,  a  derivative  of  the  eleidin  of  the  stratum  lucidum.  Nuclei 
are  lost,  but  in  many  of  the  cells  can  be  seen  the  spaces  which  the 
nuclei  once  occupied.  Constant  desquamation  of  these  cells  goes  on, 
cells  from  the  deeper  layers  taking  their  place. 

The  color  of  the  skin  in  the  white  races  is  due  to  pigmentation  of 
the  deeper  layers  of  the  epidermis.  In  certain  parts  of  the  body  pig- 
mentation of  the  connective-tissue  cells  of  the  derma  also  occurs.  In 
the  dark  races  all  cells  of  the  epidermis  are  pigmented,  although  there  is 
less  pigment  in  the  surface  cells  than  in  the  cells  more  deeply  situated. 

Two  kinds  of  glands  occur  in  the  skin — sebaceous  glands  and 
sweat  glands. 

Sebaceous  Glands.— These  are  usually  associated  with  the  hair 
follicles,  and  will  be  described  in  that  connection.  Sebaceous  glands 
unconnected  with  hair  occur  along  the  margin  of  the  lips,  in  the  glans 
and  prepuce  of  the  penis,  and  in  the  labia  minora. 

Sweat  Glands  (glandulcE  sudor ipavcp). — These  are  found  through- 
out the  entire  skin  with  the  exception  of  the  margin  of  the  lips,  the 
inner  surface  of  the  prepuce,  and  the  glans  penis.  They  are  simple 
coiled  tubular  glands.  The  coiled  portion  of  the  gland  usually  lies 
in  the  subcutis,  although  it  may  lie  wholly  or  partly  in  the  deeper 
portion  of  the  pars  reticularis.  The  excretory  duct  runs  a  quite 
straight  course  through  the  derma,  and  enters  the  epidermis  in  one 
of  the  depressions  between  the  papillae.  In  the  epidermis  the  duct 
takes  a  spiral  course  to  the  surface,  where  it  opens  into  a  minute 
pit  just  \dsible  to  the  naked  eye — the  sweat  pore  (Fig.  245 ,  p) .  The  coiled 
portion  of  the  gland  is  lined  with  a  simple  cuboidal  epithelium,  having 
a  granular  protoplasm.  In  the  smaller  glands  the  epithelium  rests 
directly  upon  the  basement  membrane.  In  the  larger  glands  a  longi- 
tudinal layer  of  smooth  muscle  cells  separates  the  glandular  epithelium 
from  the  basement  membrane.  The  walls  of  the  ducts  consist  of 
two  or  three  layers  of  cuboidal  epithelial  cells,  resting  upon  a  delicate 
basement  membrane,  outside  of  which  are  longitudinally  disposed 
connective-tissue  fibres.  On  reaching  the  horny  layer  the  epithelial 
wall  of  the  duct  ceases,  the  duct  consisting  of  a  mere  channel  through 
the  epithelium.     (Fig.  245.) 

TECHNIC. 

(i)  Fix  the  volar  half  of  a  finger-tip  in  formalin-M tiller's  fluid  (technic  5,  p. 
7)  or  in  absolute  alcohol.     Curling  may  be  prevented  by  pinning  to  a  piece  of 


356 


THE  ORGANS. 


cork.  Sections  are  cut  transversely  to  the  ridges,  stained  with  haematoxyhn-picro- 
acid-fuchsin  (technic  3,  p.  19),  and  mounted  in  balsam.  Thick  sections  should  be 
cut  for  the  study  of  the  coil  glands  with  their  ducts;  thin  sections  for  cellular  de- 
tails of  the  layers. 

(2)  Prepare  in  the  same  manner  and  for  contrast  with  the  preceding,  sections 
of  thin  skin  from  almost  any  part  of  the  body. 

(3)  Prepare  a  piece  of  negro  skin  in  the  same  manner  and  note  the  position  of 
the  pigment. 

The  Nails. 

The  nails  are  modified  epidermis.  Each  nail  consists  of:  (a)  a 
body,  the  attached  uncovered  portion  of  the  nail;  (6)  2i  free  edge,  the 
anterior  unattached  extension  of  the  body;  [c)  the  nail  root,  the  pos- 
terior part  of  the  nail  which  lies  under  the  skin  (Fig.  248). 


e       d 


Fig.  248. — Longitudinal  .Section  through  Root  of  Human  Xail  and  Nail  Bed.  X  10. 
(Schaper.)  a,  Body  of  nail;  b,  free  edge;  c,  root  of  nail;  d,  epidermis;  e,  eponychium; 
/,  stratum  germinativum  of  nail;  g,  folds  in  derma  of  nail  bed;  h,  bone  of  finger;  k, 
hyjjrjnyrhium. 


The  nail  lies  ujjon  a  specially  modified  jjortion  of  the  corium,  the 
nail  bed,  which  beneath  the  nail  root  and  somewhat  forward  of  the 
root  is  known  as  the  matrix.  The  nail  bed  is  bounded  on  either  side 
by  folds  of  skin,  the  nail  wall,  while  between  the  nail  wall  and  the 
nail  bed  is  a  furrow,  the  nail  groove  (Fig.  249). 

'J'he  nail  bed  consists  of  corium.     Its  connective-tissue  fibres  are 


THE  SKIN  AND  ITS  APPENDAGES. 


35/ 


arranged  partly  horizontal  to  the  long  axis  of  the  nail,  partly  in  a 
vertical  plane  extending  from  the  periosteum  to  the  nail.  Papillae 
are  not  present,  but  in  their  place  are  minute  longitudinal  ridges, 


Fig.  24q. — Transverse  Section  of  Nail  and  Nail  Bed.     (Rannie.)     n.  Nail;  a,  epidermis; 
p,  nail  wall,  to  inner  side  of-  which  is  the  nail  groove;  /,  folds  of  derma;  d,  nail  bed. 

which  begin  at  the  matrix  and,  increasing  in  height  as  they  pass  for- 
ward, terminate  abruptly  at  the  end  of  the  nail  bed,  beyond  which 
are  the  usual  papillae  of  the  derma. 


ifc  '•<=»'  'v-i?*  au.y 
,*'     sir  ^v^jijy  &,, 


v3?^ 


Fig.    250. — \'ertical  Transverse  Section   through  Nail  Binl\ .      X  2S0.     ^S/.ymono\\  icz.) 
a,  Nail;  b,  stratum  germinativum;  c,  ridge  of  nail  bed;  d,  derma;  e,  blood-vessel. 

The  nail  itself  consists  of  two  parts^ — an  outer  harder  part  or  true 
nail,  and  an  under  softer  part.  The  outer  portion  is  hard  and  horny, 
is  developed  from  the  stratum  lucidum,  and  consists  of  several  layers 

^  Another  division  of  nail  and  nail  bed  considers  the  nail  as  composed  of  the  hard 
part  only,  the  soft  stratum  germinativum  being  considered  a  part  of  the  nail  bed. 


358  THE  ORGANS. 

of  clear,  flat,  nucleated  cells.  These  layers  overlap  in  such  a  manner 
that  each  layer  extends  a  little  farther  forward  than  the  layer  above. 
The  under  softer  portion  of  the  nail  corresponds  to  the  stratum 
germinativum  of  the  skin  and,  like  the  latter,  consists  of  polygonal 
"prickle"  cells  and  a  stratum  cylindricum  resting  upon  a  basement 
membrane.  In  the  matrix  where  the  process  of  nail  formation  is 
going  on,  this  layer  is  thicker  than  elsewhere  and  is  white  and  opaque 
from  the  presence  of  keratohyalin.  The  convex  anterior  margin  of  this 
area  can  be  seen  with  the  naked  eye  and  is  known  as  the  lunula. 

At  the  junction  of  nail  and  skin,  in  the  nail  groove,  the  stratum 
corneum  extends  somewhat  oxtr  the  nail  as  its  eponychium.  A  simi- 
lar extension  of  the  stratum  corneum  occurs  on  the  under  surface  of 
the  nail  where  the  nail  becomes  free  from  the  nail  bed.  This  is 
known  as  the  hyponychium  (Fig.  248). 

Growth  of  nail  takes  place  by  a  transformation  of  the  cells  of  the 
matrix  into  true  nail  cells.  In  this  process  the  outer  hard  layer  is 
pushed  forward  over  the  stratum  germinativum,  the  latter  remaining 
always  in  the  same  position. 

TECHNIC. 

(i)  Remove  two  or  more  distal  phalanges  from  the  fingers  of  a  new-born  child 
and  fix  in  absolute  alcohol  or  in  formalin-MuUer's  fluid  (technic  5,  p.  7).  After 
fixing,  the  bone  should  be  carefully  removed.  Both  longitudinal  and  transverse 
sections  are  made,  stained  with  haematoxylin-picro-acid-fuchsin  (technic  3,  p.  19), 
and  mounted  in  balsam.  In  cutting  the  sections  it  is  usually  best  so  to  place  the 
block  that  the  knife  passes  through  volar  surface  first,  through  nail  last. 

(2)  The  cellular  elements  of  nail  do  not  show  well  in  sections.  For  demon- 
strating the  nail  cells,  boil  a  piece  of  nail  in  concentrated  potash  lye  or  warm  it  in 
strong  sulphuric  acid,  scrape  off  cells  from  the  softened  surface,  and  mount  in 
glycerin. 

The  Hair. 

The  hair,  like  the  nail,  is  a  development  of  the  epidermis.  The 
hair  itself  consists  of  a  shaft,  that  portion  of  the  hair  which  projects 
above  the  skin,  and  a  root,  that  portion  embedded  within  the  skin.  At 
its  lower  end  the  root  presents  a  knob-like  expansion,  the  hair  bulb, 
in  the  under  surface  of  which  is  a  cup-like  depression,  which  receives 
an  extension  of  corium.  This  is  known  as  the  papilla.  Enclosing 
the  hair  root  is  the  hair  follicle. 

The  Hair. — This  is  composed  of  epithelial  cells  arranged  in 
three  layers,  which  from  within  outward  are  medulla,  cortex,  and 
cuticle  (Fig.  252 j. 

(i)  The  medulla  occupies  the  central  axis  of  the  hair.     It  is  absent 


THE  SKIX  AND  ITS  APPENDAGES. 


359 


in  small  hairs,  and  in  the  large  hairs  does  not  extend  throughout 
their  entire  length.  It  is  from  i6  to  2o/.<  in  diameter,  and  consists  of 
from  two  to  four  layers  of  polygonal  or  cuboidal  cells  with  finely  granu- 
lar, usually  pigmented  protoplasm  and  rudimentary  nuclei. 

(2)  The  cortex  makes  up  the  main 
bulk  of  the  hair  and  consists  of  several 
layers  of  long  spindle-shaped  cells,  the 
protoplasm  of  which  shows  distinct 
longitudinal  striations,  while  the  nuclei 
appear  atrophied.  As  these  striations 
give  the  hair  the  appearance  of  being 
composed  of  fibrillse,  the  term  "corti- 
cal fibres"  has  been  applied  to  them. 
In  colored  hair,  pigment,  granules  and 
pigment  in  solution  are  found  in  and 
between  the  cells  of  this  layer.  This 
pigment  determines  the  color  of  the 
hair.  In  the  root  the  cortical  cells  are 
less  flattened  than  in  the  shaft. 

(3)  The  cuticle  has  a  thickness  of 
about  i/(,  and  consists  of  clear  scale- 
like, non-nucleated  epithelial  cells. 
These  overlap  one  another  like 
shingles  on  a  roof,  gi^'ing  to  the  sur- 
face of  the  hair  a  serrated  appear- 
ance (Fig.  252.) 

The  Hair  Follicle. — This  is  also 
a  modification  of  the  skin.  In  the 
formation  of  the  follicles  of  the  finer 
(lanugo)  hairs  the  epidermis  alone  is 
concerned.  The  follicles  of  the  larger 
hairs  contain  both  epidermal  and 
dermal  elements.  The  latter  form  the 
connective-tissue  follicle,  while  the  epidermis  forms  the  root  sheaths. 

(i)  The  root  sJieath  consists  of  two  sub-layers — the  i>i>!cr  root 
sheath  and  the  outer  root  sheath  (Figs,  253,  254,    and  255). 

(a)  The  inner  root  sheath  consists  of  three  layers,  which  from  within 
outward  are  the  cuticle  of  the  root  sheath,  Huxley's  layer,  and  Henle's 
layer. 

The  cuticle  of  the  root  sheath  lies  against  the  cuticle  of  the  hair  and 


Fig.  2 


Longitudinal  Section  of  Hair 
and  its  Follicle  from  Vertical  Section 
of  Scalp.  (Ranvier.)  a,  Shaft  of 
hair;  b,  derma;  c,  arrector  pili  muscle; 
d,  sebaceous  gland;  e,  outer  root 
sheath;  /,  inner  root  sheath;  g,  con- 
nective-tissue follicle:  h,  vitreous 
membrane;  /,  hair  bulb:  7.  papilla;  s, 
epidermis. 


360 


THE  ORGANS. 


is  similar  to  the  latter  in  structure.  It  consists  of  thin  scale-like  over- 
lapping cells,  nucleated  in  the  deeper  parts  of  the  sheath,  non-nucleated 
nearer  the  surface  (Figs.  253,  254  and  255,  c). 

Huxley's  layer  lies  immediately  outside  the  cuticle  of  the  root 
sheath,  constituting  the  middle  layer  of  the  inner  root  sheath.  It 
consists  of  about  two  rows  of  elongated  cells  with  slightly  granular 
protoplasm  containing  eleidin.     In  the  deeper  portion  of  the  root  these 

cells  contain  nuclei.     Nearer  the  surface 
°        ^         ^  the   nuclei   are   rudimentary    or  absent 
(Figs.  253,  254  and  255,  d). 

Henle's  layer  is  a  single  row  of  clear 
flat  cells.  In  the  bulb  these  cells  may 
contain  nuclei;  elsewhere  they  are  non- 
nucleated  (Fig.  255,  e) . 

(b)  The  outer  root  sheath  is  derived 
from  the  stratum  germinativum  to  which 
it  corresponds  in  structure.  Next  to  the 
\'itreous  membrane  is  a  single  layer  of 
columnar  cells  (stratum  cylindricum). 
Inside  of  this  are  several  layers  of 
"prickle"    cells     (Figs.     253,    254   and 

(2)  The  connective-tissue  follicle  con- 
sists of  three  layers — an  inner  vitreous 
membrane,  a  middle  vascular  layer,  and 
an  outer  fibrous  layer. 

(a)  The  vitreous  or  hyaline  membrane  is  a  thin  homogeneous 
structure  of  the  nature  of  an  elastic  membrane.  It  lies  next  to  the  outer 
root  sheath  and  corresponds  to  the  basement  membrane  of  the  derma 
(Figs.  253,  254  and  255,^). 

(b)  The  middle  or  vascular  layer  is  composed  of  fine  connective- 
tissue  fibres,  the  general  arrangement  of  which  is  circular.  Cellular 
elements  are  quite  abundant,  while  elastic  fibres  are,  as  a  rule,  absent. 
As  its  name  would  indicate,  this  layer  is  especially  rich  in  blood- 
vessels (Figs.  253,  254  and  255,  f). 

(c)  The  outer  or  fibrous  layer  consists  of  rather  coarse,  loosely 
woven  bundles  of  white  fibres,  which  run  mainly  in  a  longitudinal 
direction.  Among  these  are  elastic  fibres  and  a  few  connective-tissue 
cells. 

In  the  deeper  portion  of  the  root,  -some  little  distance  above  the 


Fig.  252. — Longitudinal  Section 
of  Hair.  X  350.  (KoUiker.)  a, 
Medulla;  b,  cortex;  c,  cuticle. 


THE  SKIN  AND  ITS  APPENDAGES. 


361 


bulb,  all  the  layers  of  the  hair  and  its  follicle  can  be  distinctly  seen. 
The  differentiation  of  the  layers  becomes  less  marked  as  one  passes 
in  cither  direction.  At  about  the  level  of  the  entrance  of  the  ducts 
of  the  sebaceous  glands  (see  p.  362)  the  inner  root  sheath  disappears, 
and  the  outer  root  sheath  passes  over  into  the  stratum  germinativum 
of  the  skin,  while  between  the  outer  root  sheath  (now  stratum  germi- 


FlG.  2 
(Kolliker.) 
inner  root 
membrane: 


53. — Longitudinal  Section  of  Lower  End  of  Root  of  Hair,  including 
a,  Root  of  hair;  b,  cuticle  of  hair;  c,  cuticle  of  root  sheath;  d,  Huxley's 
sheath;  e,  Henle's  layer  of  inner  root  sheath;/,  outer  root  sheath;  g, 
;  ;',  connective-tissue  follicle;  k,  bulb  of  hair;  p,  papilla. 


Papilla, 
layer  of 
vitreous 


nati\um)  and  the  hair  are  interposed  the  outer  layers  of  the  skin, 
stratum  granulosum  and  stratum  lucidum,  when  present,  and  stratum 
corneum.  x^ll  of  these  are  continuous  with  the  same  layers  of  the 
skin.  In  the  region  of  the  bulb  the  outer  root  sheath  first  becomes 
thinner,  then  disappears,  while  the  layers  of  the  inner  root  sheath 
retain  their  identity  until  the  neck  of  the  papilla  is  reached,  at  which 
point  the  different  layers  coalesce. 

The  arrector  pill  j}u{sclc  (Fig.  251,  c)  is  a  narrow  band,  or  bands,  of 
smooth  muscle  connected  with  the  hair  follicle.     It  arises  from  the 


362 


THE  ORGANS. 


outer  layer  of  the  derma  on  the  side  toward  which  the  hair  slants,  and 
is  inserted  into  the  wall  of  the  follicle  at  the  junction  of  its  middle 
and  lower  thirds,  the  sebaceous  gland  being  usually  included  between 
the  muscle  and  the  hair  (see  below).  The  contraction  of  the  muscle 
thus  tends  to  straighten  the  hair  and  to  compress  the  gland. 

The  sebaceous  glands  are  with  few  exceptions  connected  with  the 
hair  follicles.     They  are  simple  or  branched  alveolar  glands.     The 


Fig.  254. — Transverse  Section  through  Root  of  Hair  and  Hair  Follicle.  (Kolliker.) 
a,  Hair;  b,  hair  cuticle;  c,  cuticle  of  root  sheath;  d,  Huxley's  layer;  e,  Henle's  layer;/, 
outer  root  sheath;  /,  connective-tissue  follicle. 


size  of  the  gland  bears  no  relation  to  the  size  of  the  hair,  the  largest 
glands  being  frequently  connected  with  the  smallest  hairs.  The 
glands  are  spherical  or  oval  in  shape  and  each  gland  is  enclosed  by  a 
connective-tissue  capsule  derived  from  the  follicle  or  from  the  derma. 
Beneath  the  capsule  is  a  basement  membrane  continuous  with  the 
vitreous  membrane  of  the  follicle.  The  wide  excretory  duct  empties 
into  the  upper  third  of  the  follicle  and  is  lined  with  stratified  squamous 
epithelium  continuous  with  the  outer  root  sheath  and  stratum  ger- 
minativum.  The  lower  end  of  the  duct  opens  into  several  simple  or 
branched  alveoli,  at  the  mouths  of  which  the  epithelium  becom.es 
reduced  to  a  single  layer  of  cuboidal  cells.     In  the  alveoli  them.selves 


THE  SKIX  AND  ITS  APPENDAGES. 


363 


J 


A 


B 


►^sar 


■■£^^ 


the  cells  are  spheroidal  or  polyhedral,  and  usually  fill  the  entire  alveolus. 
These  cells,  like  those  lining  the  duct,  are  derivatives  of  the  outer  root 
sheath.  The  secretion  of  the  gland — an  oily  substance  called  sebum — 
appears  to  be  the  direct  product  of  disintegration  of  the  alveolar  cells, 
which  can  usually  be  seen  in  all  scares  of 
the  process  of  transformation  of  the  cell 
into  the  secretion  of  the  gland.  The 
most  peripheral  cells  show  the  least 
secretory  changes,  containing  a  few  small 
fat  droplets.  The  central  cells  and  these 
in  the  lum.en  of  the  duct  show  the  most 
marked  changes,  their  protoplasm  being 
almost  wholly  converted  into  fat,  their 
nuclei  shrunken  or  disintegrated  or  lost. 
In  the  middle  zone  are  cells  showing  in- 
termediary stages  in  the  process. 

Shedding  of  hair  occurs  in  most 
mammalia  at  regularly  recurring  periods. 
In  man  there  is  a  constant  death  and 
replacement  of  hair.  In  a  hair  about 
to  be  shed,  the  bulb  becomes  cornified 
and  splits  up  into  a  number  of  fibres. 
The  hair  next  becom.es  detached  from 
the  papilla  and  from  the  root  sheath  and 
is  cast  off,  the  empty  root  sheaths  collaps- 
ing and  forming  a  cord  of  cells  between 
the  papilla  and  lower  end  of  the  shed- 
ding hair.  If  the  dead  hair  is  to  be  re- 
placed by  a  new  one,  there  sooner  or 
later  occurs  a  proHferation  of  the  cells  of 
the  outer  root  sheath  in  the  region  of 
the  old  papilla.  From  this  "hair  germ" 
the  new  hair  is  formed  in  a  manner 
similar  to  embryonal  hair  formation, 
the  new  hair  growing  upward  under  or  to  one  side  of  the  dead  hair, 
which  it  finally  replaces. 

As  to  the  manner  in  which  growth  of  hair  lakes  place,  two  \-iews 
are  held.  According  to  one  of  these,  the  hair,  cuticle,  and  inner 
root  sheath  are  replenished  by  proliferation  of  the  epithelial  cells 
surrounding  the  papilla.     These  parts  thus  grow  from  below  toward 


Fig.  255. — From  Lungiludinal  Sec- 
tion through  Hair  and  Hair 
Follicle.  Enlarged  to  800  diame- 
ters. (Schafer.)  A,  Hair.  a, 
Cortex  of  hair;  /),  cuticle  of  hair. 
B,  Inner  sheath,  c,  Cuticle  of 
root  sheath;  d,  Hu.xley's  layer;  e, 
Henle's  layer;  /,  outer  root 
sheath  ;  ^§^,  vitreous  membrane;  i, 
connective-tissue  follicle;  »;,  fat 
cells. 


364  THE  ORGANS. 

the  surface.  The  oldest  cells  of  the  outer  root-sheath,  on  the  other 
hand,  lie  against  the  vitreous  membrane,  so  that  growth  of  this  sheath 
takes  place  from  without  inward.  According  to  the  second  view,  the 
various  parts  of  the  hair  and  its  follicle  are  direct  derivatives  of  the 
different  layers  of  the  skin,  and  their  growth  takes  place  by  a  contin- 
uous process  of  invagination.  Thus  the  most  peripheral  cells  of  the 
outer  root-sheath— stratum  cylindricum — pass  over  the  papilla  and 
turn  upward  to  form  the  medulla  of  the  hair;  the  deeper  cells — stratum 
spinosum — of  the  outer  root-sheath  become  continuous  with  the  cortex 
of  the  hair;  the  stratum  lucidum,  with  the  sheath  of  Henle,  which 
turns  up  on  the  hair  as  its  cuticle;  Huxley's  layer,  with  the  cuticle  of 
the  inner  root-sheath.  According  to  this  \dew  growth  of  hair  is 
accomplished  by  continuous  growth  downward  from  the  surface,  and 
turning  up  into  the  hair,  of  these  layers. 

TECHNIC. 

Pin  out  small  pieces  of  human  scalp  on  cork  and  fix  in  absolute  alcohol  or 
in  formalin-Mliller's  fluid  (technic  5,  p.  7).  From  one  block  cut  sections  perpen- 
dicular to  the  surface  of  the  scalp  and  in  the  long  axes  of  the  hair  and  follicles. 
From  a  second  block  cut  sections  at  right  angles  to  the  hair  follicles,  i.e.,  not  quite 
parallel  to  the  surface  of  the  scalp  but  a  little  obliquely.  By  this  means  not  only 
are  transverse  sections  secured,  but  if  the  block  be  sufficiently  long  the  follicles  are 
cut  through  at  all  levels.  Sections  are  stained  with  haematoxylin-picro-acid- 
fuchsin  (technic  3,  p.  19)  and  mounted  in  balsam. 

Blood-vessels  of  the  skin.  From  the  larger  arteries  in  the  subcu- 
taneous tissue  branches  penetrate  the  pars  reticularis  of  the  derma, 
where  they  anastomose  to  form  cutaneous  networks.  The  latter  give 
off  Ijranches,  which  pass  to  the  papillary  layer  of  the  derma  and  there 
form  a  second  series  of  networks,  the  subpapillary,  just  beneath  the 
papillae.  From  the  cutaneous  networks  arise  two  sets  of  capillaries, 
one  supplying  the  fat  lobules,  the  other  supplying  the  region  of  the 
sweat  glands.  From  the  subpapillary  networks  are  given  off  small 
arteries  which  break  up  into  capillary  networks  for  the  supply  of  the 
]ja]jillce,  sebaceous  glands,  and  hair  follicles.  The  return  blood  from 
these  capillaries  first  enters  a  horizontal  plexus  of  veins  just  under 
the  papillce.  This  communicates  with  a  second  plexus  just  beneath 
the  first.  Small  veins  from  this  second  plexus  pass  alongside  the 
arteries  to  the  deeper  part  of  the  corium,  where  they  form  a  third 
]j]exus  with  larger,  more  irregular  meshes.  Into  this  ])lexus  pass 
most  of  the  veins  from  the  fat  lobules  and  sweat  glands,  although  one 
or  two  small  veins  from  the  sweat  glands  usually  follow  the  duct  and 


THE  SKIN  AND  ITS  APPENDAGES.  365 

empty  into  the  subpapillary  plexus.  The  blood  next  passes  into  a 
fourth  plexus  in  the  subcutaneous  tissue,  from  which  arise  veins  of 
considerable  size.     These  accompany  the  arteries. 

Small  arteries  from  the  plexuses  of  the  skin  and  subcutis  pass  to 
the  hair  follicle.  The  larger  arterioles  run  longitudinally  in  the  outer 
layer  of  the  follicle.  From  these  are  given  off  branches  which  form 
a  rich  plexus  of  small  arterioles  and  capillaries  in  the  vascular  layer 
of  the  follicle.  Capillaries  from  this  plexus  also  pass  to  the  sebaceous 
glands,  the  arrectores  pilorum  muscles,  and  the  papillae. 

The  lymphatics  of  the  skin.  These  begin  as  clefts  in  the  papillse. 
which  open  into  a  horizontal  network  of  lymph  capillaries  in  the 
pars  papillaris.  This  communicates  with  a  network  of  larger  lymph 
capillaries  with  wider  meshes  in  the  subcutaneous  tissue.  The  latter 
also  receives  lymph  capillaries  from  plexuses  which  surround  the  seba- 
ceous glands,  the  sweat  glands,  and  the  hair  follicles. 

The  nerves  of  the  skin.  These  are  mainly  sensory.  Efferent 
sympathetic  axones  supply  the  smooth  muscle  of  the  walls  of  the  blood- 
vessels, the  arrectores  pilorum,  and  secretory  fibres  to  the  sweat  glands. 
The  medullated  sensory  nerves  are  peripheral  processes  of  spinal  gang- 
lion cells.  The  larger  trunks  lie  in  the  subcutis,  giving  off  branches 
which  pass  to  the  corium,  where  they  form  a  rich  subpapillary  plexus  of 
both  medullated  and  non-medullated  fibres.  From  the  subcutaneous 
nerve-trunks  and  from  the  subpapillary  plexus  are  given  off  fibres  which 
terminate  in  more  or  less  elaborate  special  nerve  endings  (see  page  386) . 
Their  location  is  as  follows:  (i)  In  the  subcutis:  Vater-Pacinian  corpus- 
cles, the  corpuscles  of  Ruffini,  and  the  Golgi-Mazzoni  corpuscles  of  the 
finger-tip.  The  first  two  forms  are  most  numerous  in  the  palms  and 
soles.  (2)  In  the  derma:  Tactile  corpuscles  of  Meissner  and  Wagner. 
These  are  found  in  the  papillae,  especially  of  the  finger-tip,  palm,  and 
sole.  Krause's  end  bulbs — usually  in  the  derma  just  beneath  the 
papillae,  more  rarely  in  the  papillae  themselves.  (3)  In  the  epithelium: 
Free  nerve  endings  among  the  epithelial  cells. 

Branches  of  the  cutaneous  nerves  supply  the  hair  follicles.  As  a 
rule  but  one  nerve  passes  to  each  follicle,  entering  it  just  below  the 
entrance  of  the  duct  of  the  sebaceous  gland.  As  it  enters  thefolhclc 
the  nerve  fibre  loses  its  medullary  sheath  and  divides  into  two  branches, 
which  further  subdivide  to  form  a  ring-like  plexus  of  fine  fibres  encir- 
cling the  follicle.  From  this  ring,  small  varicose  fibrils  run  for  a  short 
distance  up  the  follicle,  terminating  mainly  in  slight  expansions  on  the 
vitreous  membrane. 


366  THE  ORGANS. 


TECHNIC. 


For  the  study  of  the  blood-vessels  of  the  skin  inject  (technic  p.  22)  the  entire 
hand  or  foot  of  a  new-born  child.  E.xamine  rather  thick  sections  either  mounted 
unstained  or  stained  only  with  eosin. 

Development  of  the  Skin,  Nails,  and  Hair. 

The  epidermis  is,  as  already  noted,  of  ectodermic  origin.  It  con- 
sists at  first  of  a  single  layer  of  cuboidal  cells.  This  soon  differen- 
tiates into  two  layers — an  outer,  the  future  stratum  corneum,  and  an 
inner,  the  future  stratum  germinativum.  The  stratum  granulosum 
and  stratum  lucidum  are  special  developments  of  the  stratum  germi- 
nativum. The  corium  is  of  mesoblastic  origin.  It  is  at  first  smooth, 
the  papillae  being  a  secondary  development. 

The  nail  first  appears  as  a  thickening  of  the  stratum  lucidum. 
This  spreads  until  the  future  nail  bed  is  completely  covered.  During 
development  the  stratum  corneum  extends  completely  over  the  nail 
as  its  eponychium.  During  the  ninth  month  (intra-uterine)  the  nail 
begins  to  grow  forward  free  from  its  bed  and  the  eponychium  disap- 
pears, except  as  already  noted. 

The  hair  also  develops  from  ectoderm.  It  first  appears  about  the 
end  of  the  third  foetal  month  as  a  small  local  thickening  of  the  epidermis. 
This  thickening  is  due  mainly  to  proliferation  of  the  cells  of  the  stratum 
mucosum,  and  soon  pushes  its  way  down  into  the  underlying  corium, 
forming  a  long  slender  cord  of  cells — the  hair  germ.  Differentiation 
of  the  surrounding  connective  tissue  of  the  corium  forms  the  follicle 
w^all,  while  an  invagination  of  this  connective  tissue  into  the  lower  end 
of  the  hair  germ  forms  the  papilla.  The  cells  of  the  hair  germ  now 
differentiate  into  two  layers:  a  central  core  the  middle  portion  of  which 
forms  the  hair,  while  the  peripheral  portion  forms  the  inner  root  sheath; 
and  an  outer  layer  which  becomes  the  outer  root  sheath.  The  sublayers 
are  formed  from  these  by  subsequent  differentiation.  The  hair  when 
first  formed  lies  wholly  beneath  the  surface  of  the  skin.  As  the  hair 
reaches  the  surface  its  pointed  extremity  pierces  the  surface  epithelium 
to  become  the  hair  shaft  (Fig.  256). 

The  sebaceous  gland  develops  as  an  outgrowth  from  the  outer  root 
sheath.  This  is  a  flask-shaped  and  at  first  solid  mass  of  cells,  which 
later  differentiate  to  form  the  ducts  and  alveoli  of  the  gland. 

The  sweat  glands  first  appear  as  solid  ingrowths  of  the  stratum 
germinativum  into  the  underlying  corium.  The  lower  end  of  the 
ingrowth  becomes  thickened  and  convoluted  to  form  the  coiled  por- 


THE  SKIN  AND  ITS  APPENDAGES. 


367 


III 


Fig  256 —Five  stages  in  the  development  of  a  human  hair.  (Stohr  )  <;Pinill-v 
&  arrector  pih  muscle;  c,  beginning  of  hair  shaft;  ^,  point  whe^ ha  r  shaf  throws 
hrough  epidermis;  .,  anlage  of  sebaceous  gland;  /,  hair'  germ;   e    "air    haft    rH?r's 

r/tl-'  ?"■'''<?  ^^■''■'  ^'  '""'''^^  °^  ^°°^  ^1^^^'h;  /,  in'ner    oS    h^at    ;  ,/  outer  roo? 
sheath  m  tangential  section;  n,  outer  root  sheath;  o,  connective-tissue  fol  ic  e 


368  THE  ORGANS. 

tion  of  the  gland,  and  somewhat  later  the  central  portion  becomes 
channelled  out  to  form  the  lumen.  The  muscle  tissue  of  the  sweat 
glands,  which  lies  between  the  epithelium  and  the  basement  mem- 
brane, is  the  only  muscle  of  the  body  derived  from  the  ectoderm. 

The  Mammary  Gland. 

The  mammary  gland  is  a  compound  alveolar  gland.  It  consists 
of  from  fifteen  to  twenty  lobes,  each  of  which  is  subdivided  into 
lobules.  The  gland  is  surrounded  by  a  layer  of  connective  tissue 
containing  more  or  less  fat.  From  this  periglandular  connective 
tissue  broad  septa  extend  into  the  gland,  separating  the  lobes  (inter- 
lobar septa).  From  the  latter  finer  connective-tissue  bands  pass 
in  between  the  lobules  (interlobular  septa).  From  the  interlobular 
septa  strands  of  connective  tissue  extend  into  the  lobule  where  they 
act  as  support  for  the  glandular  structures  proper.  An  excretory  duct 
passes  to  each  lobe  where  it  divides  into  a  number  of  smaller  ducts 
(lobular  ducts),  one  of  which  runs  to  each  lobule.  Within  the  latter 
the  lobular  duct  breaks  up  into  a  number  of  terminal  ducts,  which  in 
turn  open  into  groups  of  alveoli.  The  fifteen  to  twenty  main  excre- 
tory ducts  pass  through  the  nipple  and  open  on  its  surface.  At  the 
base  of  the  nipple  each  main  duct  presents  a  sac-like  dilatation,  the 
ampulla,  which  appears  to  act  as  a  reservoir  for  the  storage  of  the  milk. 

Until  puberty  the  gland  continues  to  develop  alike  in  both  sexes, 
but  after  about  the  twelfth  year  the  male  gland  undergoes  retrogressive 
changes,  while  the  female  gland  continues  its  development. 

The  inactive  mammary  gland,  by  which  is  meant  the  female 
gland  up  to  the  advent  of  the  first  pregnancy  and  between  periods  of 
lactation,  consists  mainly  of  connective  tissue  and  a  few  scattered 
groups  of  excretory  ducts  (Fig.  257).  Around  the  ends  of  some  of 
the  ducts  are  small  groups  of  collapsed  alveoli.  Both  ducts  and 
alveoli  are  lined  with  a  low  columnar,  often  rather  flat  epithelium.  In 
some  cases  the  flat  cells  are  two  or  three  layers  thick,  forming  a  thin 
stratified  squamous  epithelium.  The  relative  amount  of  fat  and 
connective  tissue  varies  greatly,  some  inactive  mammae  consisting 
almost  wholly  of  fat  tissue. 

The  Active  Mammary  Gland. — Throughout  pregnancy  the 
gland  undergoes  extensive  developmental  changes  and  becomes  func- 
tional at  about  the  time  of  birth  of  the  child.  The  microscopic  ap- 
pearance of  the  active  gland  differs  greatly  from  that  of  the  inactive 


THE  SKIN  AND  ITS  APPENDAGES.  309 

(Fig.  258).  There  is  a  marked  reduction  in  the  connective  tissue  of 
the  gland,  its  place  being  taken  by  newly  developed  ducts  and  alveoli. 
The  alveoli  are  spheroidal,  oval,  or  irregular  in  shape,  and  vary  con- 
siderably in  size.  The  alveoli  are  lined  by  a  single  layer  of  low  col- 
umnar or  cuboidal  epithelial  cells  which  rest  upon  a  homogeneous 
basement  membrane.  The  appearance  of  the  cells  differs  according 
to  their  secretory  conditions.  The  resting  cell  is  cuboidal  and  its 
protoplasm  granular.     With  the  onset  of  secretion  the  cell  elongates, 


^r6M' 


Hfi 


U^'- 


Fig.  257. — From  Section  of  Human  Inactive  Mammary  Gland.      X  25.  (Technic  i,  p.  371.) 
Gland  composed  almost  wholly  of  connective  tissue;  few  scattered  groups  of  tubules. 

and  a  number  of  minute  fat  droplets  appear.  These  unite  to  form 
one  or  two  large  globules  of  fat  in  the  free  end  of  the  cell.  The  fat 
is  next  discharged  into  the  lumen  of  the  alveolus,  and  regeneration  of 
the  cell  takes  place  from  the  unchanged  basal  portion.  As  to  the 
number  of  times  a  cell  is  able  to  go  through  this  process  of  secretion 
and  repair  before  it  must  be  replaced  by  a  new  cell,  nothing  definite 
is  known.  Active  secretion  does  not  as  a  rule  take  place  in  all  the 
alveoli  of  a  lobule  at  the  same  time.  Each  lobule  thus  contains  both 
active  and  inacti\"e  aheoli.  The  smallest  ducts  are  lined  with  a  low 
columnar  or  cuboidal  e])ithelium.  This  increases  in  hcii^ht  with 
^4 


370 


THE  ORGAXS. 


increase  in  the  diameter  of  the  duct  until  in  the  largest   ducts   the 
epithelium  is  of  the  high  columnar  type. 

The  secretion  of  the  gland  is  milk.  This  consists  microscopically 
of  a  clear  fluid  or  plasma  in  which  are  suspended  the  milk  globules. 
The  latter  are  droplets  of  fat  from  3  to  5//  in  diameter,  each  enclosed 
in  a  thin  albuminous  membrane  which  prevents  the  droplets  from 
coalescing.  Cells,  probably  leucocytes,  containing  fat  droplets  may 
also  be  present.  In  the  secretion  of  the  gland  during  the  later  months 
of  pregnancy,  and  also  for  a  few  days  following  the  birth  of  the  child. 


Fig.  258. — From  Section  of  Human  Mammary  Gland  during  Lactation.      X  50.    (Stohr.) 
a.  Branch  of  excretory  duct;  h,   interlobular  connective  tissue;  c,  alveoli. 


a  relatively  large  number  of  large  fat-containing  leucocytes — colostrum 
corpuscles — are  found. 

Blood-vessels. — These  enter  the  gland,  branch  and  ramify  in  the 
interlobar  and  Interlobular  connective  tissue,  and  finally  terminate  in 
capillary  networks  among  the  alveoli  and  ducts.  From  the  capillaries 
arise  veins  which  accompany  the  arteries. 

Lymphatics. — Lymph  capillaries  form  networks  among  the  alveoli 
and  terminal  ducts.  The  lymph  capillaries  empty  into  larger  lymph- 
atics in  the  connective  tissue.  These  in  turn  communicate  with 
several  lymph  \'esse]s  which  convey  the  lymjjh  to  the  axillary  glands. 

Nerves. — Both  ccrebro-spinal  and  sympathetic  nerves  sup])ly  the 
gland,   the   larger  trunks  following   the   interlobar  and   interlobular 


THE   SKIX   AND   ITS   APPENDAGES. 


371 


connective-tissue  septa.  The  nerve  terminals  break  up  into  plexuses 
which  surround  the  alveoli  just  outside  their  basement  membranes. 
From  these  plexuses,  delicate  fibrils  have  been  described  passing 
through  the  basement  membrane  and  ending  between  the  secreting 
cells. 

Development. — The  development  of  the  mammary  gland  is  quite 
similar  to  the  development  of  the  sebaceous  glands.  The  gland  first 
appears  as  a  dipping  down  of  solid  cord-like  masses  of  cells  from  the 
stratum  mucosum.     The  alveoli  remain  rudimentary  until  the  advent 


Fig.  259. — From  Section  of  Mammary  Gland  of  Guinea-pig  during  Lactation. 
X  500.  (Osmic  acid.)  (Szymonowicz.)  a,  Basement  membrane;  h,  lumen  of  alveolus;  c, 
tangential  section  of  alveolus;  d,  fat  globules. 

of  pregnancy.  After  lactation  the  alveoli  atrophy,  being  replaced  by 
connective  tissue,  and  the  gland  returns  to  the  resting  state.  After 
the  menopause  a  permanent  atrophy  of  the  gland  begins,  fat  and  con- 
nective tissue  ultimately  almost  wholly  replacing  the  glandular 
elements. 


TECHNIC. 

(i)  Fix  thin  slices  of  an  inactive  mammary  gland  in  formalin-Miiller's  fluid 
(technic  5,  p.  7).  Stain  sections  with  hcematoxylin-eosin  (technic  i,  p.  18),  and 
mount  in  balsam. 

(2)  Prepare  sections  of  an  active  mammary  gland,  as  in  preceding  technic  (i). 


372  THE  ORGANS. 

(3)  Fix  very  thin  small  pieces  of  an  active  gland  in  one-per-cent.  aqueous  solu- 
tion of  osmic  acid.  After  twenty-four  hours  wash  in  water  and  harden  in  graded 
alcohols.  Thin  sections  may  be  mounted  unstained,  or  after  slight  eosin  stain,  in 
glycerin. 

General  References  for  Further  Study. 

Kolliker:  Handbuch  der  Gewebelehre  des  Menschen. 
McMurrick:  Development  of  the  Human  Body. 
Ranvier:  Traite  Technique  d'  Histologic. 
Schafer:  Essentials  of  Histology. 

Spalteholz:  Die  Vertheilung  der  Blutgefasse  in  der  Haut.  Arch.  Anat.  u. 
Phys.,  Anat.  Abth.,  1893. 


CHAPTER  XL 

THE  NERVOUS  SYSTEM. 

The  nervous  mechanism  in  man  consists  of  two  distinct  though 
associated  systems,  the  cerebrospinal  nervous  system  and  the  sym- 
pathetic nervous  system.  Each  of  these  systems  is  composed  of  a  central 
portion  which  is  its  centre  of  nervous  activity,  and  of  a  peripheral 
portion  which  serves  to  place  the  centre  in  connection  with  the  organs 
which  it  controls.  In  the  cerebro-spinal  system  the  central  portion  is 
known  as  the  central  nervous  system  and  consists  of  the  cerebro-spinal 
axis,  or  brain  and  spinal  cord.  The  peripheral  portion  is  formed  by 
the  cranial  and  spinal  nerves.  The  central  portion  of  the  sympathetic 
system  consists  of  a  series  of  ganglia  from  which  the  sympathetic  nerves 
take  origin.     These  latter  constitute  its  peripheral  portion. 

HISTOLOGICAL  DEVELOPMENT  AND  GENERAL 
STRUCTURE. 

The  beginning  differentiation  of  the  nervous  system  appears  very 
early  in  embryonic  life.  It  is  first  indicated  by  a  longitudinal  median 
thickening  of  the  outer  embryonic  layer  or  ectoderm,  to  form  the 
neural  plate.  The  sides  of  the  plate  become  elevated  to  form  the 
neural  folds,  leaving  between  them  the  neural  groove.  By  the  dorsal 
union  of  these  folds  the  neural  groove  is  converted  into  the  neural  lube. 
The  lumen  of  the  neural  tube  corresponds  to  the  central  canal  of  the 
cord  and  the  ventricles  of  the  brain  in  the  adult,  and  it  is  from  the 
ectodermic  cells  which  form  the  walls  of  this  tube  that  the  entire  nervous 
system  is  developed.  The  caudal  portion  of  the  tube  is  of  nearly  uni- 
form diameter — the  spinal  cord.  At  the  cephalic  end,  the  neural 
plate,  even  before  its  closure,  is  wider  and  forms,  when  closed,  an 
expanded  portion  of  the  tube,  the  brain.  In  their  further  dc^•clopment, 
the  walls  of  the  brain  form  three  expansions — ^the  three  brain  "  vesicles" 
known  as  the  forebrain  (prosencephalon),  midbrain  (mesencephalon),  and 
hindbrain  {rhombencephalon).  In  the  forebrain  two  main  divisions  are 
usually  distinguished,  the  endbrain  (tcloiccphalon)  and  the  interbrain 
(dicncephalon).     The  basal   ])art  of  the   endbrain  forms  the  corpora 

373 


374  THE  ORGANS. 

striata  and  rhinencephalon,  while  the  dorsal  part  expands  into  the 
pallium  {cerebral  hemispheres) .  In  the  interbrain  may  be  distinguished 
a  dorsal  part,  the  epithalamus;  a  middle  (largest)  part,  the  thalamus;  and 
a  ventral  expansion,  the  hypothalamus.  In  the  midbrain  the  basal  part 
becomes  the  tegmentum,  and  the  dorsal  part  expands  into  the  corpora 
quadrigemina  or  inferior  and  superior  colliculi.  The  narrower  part, 
connecting  midbrain  and  hindbrain,  is  the  isthmus.  The  basal  part 
of  the  hindbrain  forms  the  medulla  oblongata  and  part  of  the  dorsal  wall 
expands  into  the  cerebellum.  In  the  later  development  of  the  brain,  the 
pallium,  and  with  it  parts  of  the  cerebellum,  becomes  enormously 
enlarged  and  structures  are  formed  constituting  connections  between 
the  pallium  and  the  rest  of  the  brain.  The  most  massive  of  these  are 
the  pes  pedunculi,  added  ventrally  to  the  thalamus  and  midbrain; 
the  pons  Varolii,  added  ventrally  to  part  of  the  midbrain,  isthmus 
and  part  of  the  hindbrain;  and  the  pyramids,  added  ventrally  to  the 
medulla.  The  basal  part  of  the  mid-  and  hindbrain,  thus  covered 
ventrally  by  the  pes  and  pons,  is  the  tegmentum.  Other  portions  of 
the  dorsal  walls  of  the  forebrain  and  hindbrain  form  thin-walled  ex- 
pansions which,  together  with  vascular  mesodermic  coverings,  are  the 
chorioid  plexuses  of  the  lateral,  third,  and  fourth  ventricles.  The  cavi- 
ties of  the  cerebral  hemispheres  are  the  lateral  ventricles;  the  cavity 
of  the  interbrain  is  the  third  ventricle;  that  of  the  midbrain  is  the  iter 
or  aqucsductus  Sylvii;  that  of  the  hindbrain  is  the  fourth  ventricle. 

The  wall  of  the  neural  tube  is  at  first  composed  of  a  single  layer  of 
epithelial  cells.  By  proliferation  of  these  cells  the  epithelium  soon 
becomes  many-layered,  and  forms  a  syncytium — the  myelospongium  of 
His — although  some  of  the  original  epithelial  cells  appear  to  extend 
through  the  entire  thickness  of  the  wall. 

Some  of  the  syncytial  cells  which  extend  through  the  entire  thickness 
of  the  wall  of  the  neural  tube  (spongioblasts  of  His)  increase  in  length 
as  the  wall  increases  in  thickness.  The  inner  ends  of  these  cells  form 
the  lining  of  the  tube,  while  other  parts  of  the  cells  between  the  lumen 
and  the  surface  tend  to  collapse,  forming  cord-like  structures.  The 
outer  ends  of  the  cells,  on  the  other  hand,  become  perforated  and  unite 
to  form  a  thick  network — the  marginal  veil  of  His.  Of  these  cells, 
some  retain  this  position,  with  nuclei  near  the  lumen,  in  the  adult  and 
are  known  as  ependymal  cells;  others  move  away  from  the  central  canal 
and  become  neuroglia  cells. 

Still  other  of  the  cells  of  the  neural  tube  are  destined  to  become 
neurones,  and  as  such  are  known  as  neuroblasts.     From  the  neuro- 


THE  NERVOUS  SYSTEM.  375 

blast  a  neurofibrillated  process  grows  out — the  future  axone.  Den- 
drites which  at  this  stage  are  absent  develop  later  in  a  similar  man- 
ner, i.e.,  by  extensions  of  the  cell  protoplasm/  The  neuroblasts  soon 
leave  their  original  position  near  the  lumen  and  pass  outward  along 
the  spaces  between  the  elongated  ependymal  cells,  but  their  bodies 
do  not  usually  penetrate  the  marginal  veil.  Some  may,  however,  pass 
through  and  even  leave  the  neural  tube  along  with  the  efferent  roots. 
The  axones  of  many  neuroblasts  located  in  the  ventral  part  of  the  neural 
tube  pierce  the  marginal  veil  and  leave  the  neural  tube  as  the  efferent 
root  fibres.  These  pass  to  sympathetic  ganglia  or  to  various  struc- 
tures (muscles,  glandular  epithelia)  the  activities  of  which  they  affect. 
Such  structures  may  be  collectively  termed  effectors.  These  nerve 
cells  together  with  many  of  the  sympathetic  neurones  (see  below)  are 
the  efferent  peripheral  neurones.  The  axones  of  other  neuroblasts  do 
not  completely  pierce  the  marginal  veil,  but  are  directed  upward  and 
downward  within  it,  thus  forming  fibres  connecting  various  parts  of 
the  central  nervous  system.  Axones  of  still  other  neuroblasts,  espe- 
cially in  suprasegmental  structures  (see  p.  377),  are  directed  toward 
the  lumen.  All  such  neurones  whose  axones  do  not  leave  the  neural 
tube  may  be  termed  intermediate  or  central  neurones,  as  distin- 
guished from  the  peripheral  neurones:  intermediate,  because  they  serve 
as  intermediate  links  connecting,  within  the  central  nervous  system.,  the 
terminations  of  the  afferent  peripheral  neurones  (see  below)  with  the 
bodies  of  the  efferent  peripheral  neurones;  central,  because  they  are 
confined  to  the  central  nervous  system.  Later  becoming  medullated, 
their  axones  constitute  the  great  majority  of  the  fibres  of  the  white 
matter  of  the  central  nervous  system. 

During  the  closure  of  the  neural  groove,  groups  of  cells  from  the 
crest  of  each  neural  fold  become  separated  from  the  rest  of  the  develop- 
ing nervous  system.  Some  of  these  cells  form  the  cerebrospinal  ganglia, 
while,  according  to  most  authorities,  others  migrate  still  further  from 
the  neural  tube  and  form  the  various  sympathetic  ganglia.  Some  cells 
(neuroblasts)  develop  into  the  -nerve  cells  of  the  cerebro-spinal  and 
sympathetic  ganglia.  Others  form,  according  to  some  authorities,  en- 
veloping cells,  such  as  the  capsule  cells  around  the  ganglion  cell  bodies 
and  the  neurilemma  cells  around  the  peripheral  nerve  fibres.  These 
latter  would  thus  corres])ond  to  the  neuroglia  cells  of  the  central 
nervous  system.     The  majority  of  the  neuroljlasts  of  the  cerebro- 

'  Accordinn;  to  other  \ie\\s,  otlier  cells  may  participate  in  the  formation  of  the  axone, 
and  the  dendrites  may  anastomose  with  other  neuroblasts  (see  Chap.  \'I). 


376  THE  ORGANS. 

spinal  ganglia  develop  two  processes:  peripheral  processes  {afferent 
nerve  fibres)  to  ^'arious  structures  {receptors)  which  receive  stimuli; 
and  central  processes,  forming  the  afferent  roots  and  passing  into  the 
central  nervous  system  where  they  usually  bifurcate  and  form  longi- 
tudinal ascending  and  descending  arms.  These  cells  are  at  first 
bipolar,  later  the  cell  body  w^ithdraws  from  the  two  processes  and 
thus  assumes  the  adult  unipolar  condition  (see  page  383).  Other 
processes  may  also  appear.  Many  of  the  neuroblasts  of  the  sympa- 
thetic ganglia  develop  dendrites  and  axones  while  others  form  branch- 
ing cells  in  which  the  two  kinds  of  processes  cannot  be  easily 
distinguished.  Sympathetic  cells  are  also  derived  from  cells  which 
migrate  from  the  neural  tube  along  the  efferent  root  (p.  375). 

The  cerebro-spinal  ganglionic  neurones,  together  with  some  sym- 
pathetic neurones,  certain  neurones  in  the  olfactory  mucous  membrane, 
retina,  and  possibly  midbrain  roof,  constitute  the  afferent  peripheral 
neurones  of  the  entire  nervous  system.  Most  of  the  sympathetic 
neurones  are  efferent.  The  peripheral  processes  of  the  afferent  per- 
ipheral neurones,  the  axones  of  the  efferent  peripheral  neurones  after 
they  have  emerged  from  the  central  nervous  system,  and  the  axones  of 
the  sympathetic  ganglion  cells,  together  with  all  their  sheaths  and  con- 
nective-tissue investments,  form  the  peripheral  nerves.  The  bodies  of 
the  afferent  peripheral  neurones  and  sympathetic  neurones  form  groups 
known  as  ganglia.  The  peripheral  neurones  are  arranged  segmentally, 
as  shown  by  the  series  of  ganglia  and  nerves. 

The  sympathetic  neurones  and  those  cerebro-spinal  neurones 
which  innervate  sympathetic  ganglia,  viscera,  glands,  blood-vessels, 
and  smooth  and  heart  muscle  are  peripheral  visceral  or  splanchnic 
neurones.  Those  cranial  nerve  neurones  which  innervate  the  striated 
voluntary  muscles  of  jaw,  face,  pharynx,  and  larynx  are  usually  also 
classed  as  splanchnic.  The  remainder  of  the  cerebro-spinal  periph- 
eral neurones  are  peripheral  somatic  neurones. 

From  the  foregoing  it  will  be  seen  that  all  the  neurones  of  the 
nervous  system  fall  into  two  categories:  I,  Peripheral  neurones,  a 
part  of  whose  processes,  at  least,  lie  outside  the  central  nervous  sys- 
tem, forming  the  peripheral  nerves.  II,  Central  or  intermediate 
neurones.  These  lie  entirely  within  the  central  nervous  system.  The 
peripheral  neurones  may  be  classified  as  follows:  A.  Afferent  (all  the 
neurone  bodies  outside  the  central  nervous  system,  except  possibly 
some  in  midbrain  roof).  The  afferent  neurones  are  (i)  the  cerebro- 
spinal ganglion  cells,  (a)  somatic,  (b)  splanchnic;   (2)  cells  in  olfactory 


THE  NERVOUS  SYSTEM.  377 

membrane,  retina,  and  possibly  midbrain;  (3)  some  sympathetic  neu- 
rones (splanchnic).  B.  Efferent  neurones.  These  are  (i)  cerebro- 
spinal (neurone  bodies  in  ventral  part  of  central  nervous  system), 
(a)  somatic  (to  voluntary  striated  muscles),  {h)  splanchnic  (to  sympa- 
thetic ganglia,  smooth  and  heart  muscle,  glands);  (2)  sympathetic 
(splanchnic,  bodies  in  sympathetic  ganglia,  to  smooth  and  heart 
muscle,  glands). 

In  the  central  nervous  system  the  bodies  and  dendrites  are  usually 
aggregated  in  certain  localities  which,  on  account  of  their  appearance 
when  examined  in  fresh  condition,  are  collectively  termed  the  gray 
matter  [siihstantia  grisea).  The  gray  matter  also  contains  the  begin- 
nings and  endings  of  the  nerve  fibres.  The  parts  of  the  nervous 
system  where  the  bodies  and  dendrites  are  absent  and  which 
are  composed  (exclusive  of  the  neuroglia,  blood-vessels,  etc.)  of  the 
medullated  nerve  fibres  are  collectively  termed  the  ivhite  matter 
{substantia  alba). 

The  central  nervous  system  may  be  divided  into  a  segm,ental  part 
and  a  suprasegmental  part.  The  former  is  in  more  immediate  relation 
with  the  peripheral  (segmental)  nerves.  It  comprises  the  spinal  cord 
and  basal  part  of  the  brain  {segmental  brain).  It  contains  all  the 
bodies  of  the  efferent  cerebro-spinal  neurones  and  practically  all  the 
terminations  of  the  central  processes  (afferent  root  fibres)  of  the  affer- 
ent peripheral  neurones.  In  it  the  gray  matter  is  internal,  as  a  rule, 
and  the  white  matter  external.  The  suprasegmental  part  comprises 
the  expanded  portions  of  the  dorsal  wall  of  the  neural  tube  already 
mentioned,  namely  the  pallium,  corpora  quadrigemina,  and  cere- 
bellum. These  constitute  the  highest  coordinating  centers  of  the 
nervous  system.  Here  the  gray  matter  is  external,  constituting  a 
cortex,  and  the  white  matter  is  internal. 

The  grouping  of  peripheral  neurones  into  ganglia  and  nerves 
has  already  been  mentioned.  In  the  central  nervous  system  more  or 
less  definite  groups  or  systems  of  neurones  having  certain  definite  con- 
nections may  also  be  distinguished.  The  axones  of  such  a  system 
constitute  a  tract  or,  when  aggregated  into  a  definite  bundle,  Si  fascicu- 
lus. The  groups  of  neurone  bodies  are  termed  nuclei.  The  group  or 
collection  of  bodies  whose  axones  form  a  certain  tract  is  the  nucleus 
of  origin  of  that  tract.  The  same  nucleus  may  receive  the  termina- 
tions of  some  other  tract  and  is  then  the  terminal  nucleus  of  that  tract. 
A  given  neurone  system  serves  as  a  path  for  the  conduction  of  some 
particular   kind   of   nerve   impulse.     A   conduction  path,  however,  is 


378 


THE  ORGANS. 


often  composed  of  several  neurone  systems  linked  together,  thus  form- 
ing a  series  of  relays. 

All  reactions  performed  by  the  nervous  system  must  ultimately 
take  effect  upon  some  part  of  the  body  or  effector  and  are  usually  ini- 
tiated by  changes  in  some  receptor.  Such  a  circuit  from  receptor  to 
effector  may  be  termed  a  neural  arc  (Fig.  260),  and  will  involve  af- 
ferent peripheral  neurones,  efferent  peripheral  neurones  and  usually 
intermediate  neurones.     The  complexity  of  such  arcs  depends  largely 


Three  -rveicr one  a/Yer'enf ^uftrctse^me/zicil/tet/Ji 


Fig.  260. — Diagram  illustrating  an  arc  transversing  only  thie  segmental,  and  an 
arc  transversing  the  suprasegmental  part  of  the  nervous  system. 

upon  the  number  and  character  of  intermediate  neurones  intercalated 
in  the  arc  between  the  afferent  and  efferent  peripheral  neurones. 
Such  arcs  may  obviously  traverse  centrally  only  the  cord  or  segmental 
brain  or  may  also  traverse  one  or  more  of  the  suprasegmental  parts 
of  the  nervous  system.  Intermediate  neurones  which  link  together 
different  segments  of  the  cord  and  segmental  brain  may  be  termed 
intersegmental  neurones.  Other  intermediate  neurones  form  paths  to 
and  from  suprasegmental  parts  {afferent  and  efferent  suprasegmental 
neurones)  and  still  others  are  suprasegmental  associative  neurones  con- 
fined to  suprasegmental  structures  (Fig.  260). 


MEMBRANES  OF  THE  BRAIN  AND  CORD. 

The  brain  and  cord  are  enclosed  by  two  connective-tissue  mem- 
branes, the  dura  mater  and  the  pia  mater  (Fig.  261). 

The  dura  mater  is  the  outer  of  the  two  membranes  and  consists 
of  dense  fibrous  tissue.  The  cerebral  dura  serves  both  as  an  invest- 
ing membrane  for  the  brain  and  as  periosteum  for  the  inner  surfaces 
of  the  cranial  bones.  It  consists  of  two  layers:  {a)  An  inner  layer 
of   closely    packed    fibro-elastic    tissue    containing    many    connective 


THE  NERVOUS  SYSTEM. 


379 


tissue  cells,  and  lined  on  its  brain  surface  with  a  single  layer  of  flat 
cells;  and  (b)  an  outer  layer,  which  forms  the  periosteum  and  is  similar 
in  structure  to  the  inner  layer,  but  much  richer  in  blood-vessels  and 
nerves.  Between  the  two  layers  are  large  venous  sinuses.  The 
spinal  dura  corresponds  to  the  inner  layer  of  the  cerebral  dura,  which 


^   ^ 

2  c 


>    3 


U    3 

3 


5  ^ 


it  resembles  in  structure,  the  vertebras  having  their  own  .separate 
periosteum.  The  outer  surface  of  the  spinal  dura  is  covered  with  a 
single  layer  of  flat  cells,  and  is  separated  from  the  periosteum  bv  the 
epidural  space,  which  contains  anastomosing  venous  channels  Iving 
in  an  areolar  tissue  rich  in  fat. 


380  THE  ORGANS. 

The  pia  mater  closely  invests  the  brain  and  cord,  extending  into 
the  sulci  and  sending  prolongations  into  the  ventricles.  It  consists 
of  fibro-elastic  tissue  arranged  in  irregular  lamellse,  forming  a  spongy 
tissue,  the  cavities  of  which  contain  more  or  less  fluid.  The  outer 
lamellse  are  the  most  compact,  and  are  covered  on  the  dural  surface 
by  a  single  layer  of  flat  cells.  It  is  this  external  layer  of  the  pia  which 
is  frequently  described  as  a  separate  membrane,  the  arachnoid.  The 
inner  lamellae  of  the  pia  are  more  loosely  arranged,  are  more  cellular 
and  more  vascular.  Especially  conspicuous  are  large,  irregular 
cells  with  delicate  bodies  and  large  distinct  nuclei.  They  lie  upon 
the  connective-tissue  bundles  partially  lining  the  spaces. 

The  Pacchionian  bodies  are  peculiar  outgrowths  from  the  outer 
layer  of  the  pia  mater  cerebralis,  which  are  most  numerous  along 
the  longitudinal  fissure.  They  are  composed  of  fibrous  tissue,  and 
frequently  contain  fat  cells  and  calcareous  deposits. 

Blood-vessels. — The  spinal  dura  and  the  inner  layer  of  the  cere- 
bral dura  are  poor  in  blood-vessels.  The  outer  layer  of  the  cerebral 
dura,  forming  as  it  does  the  periosteum  of  the  cranial  bones,  is  rich 
in  blood-vessels  which  pass  into  and  supply  the  bones.  The  pia  is 
very  vascular,  especially  its  inner  layers,  from  which  vessels  pass 
into  the  brain  and  cord. 

TECHNIC. 

For  the  study  of  the  structure  of  the  membranes  of  the  brain  and  spinal  cord, 
fix  pieces  of  the  cord  with  its  membranes,  and  of  the  surface  of  the  brain  with  mem- 
branes attached,  in  formalin-Muller's  fluid  (technic  5,  p.  7)  and  stain  sections  with 
haematoxylin-eosin  (technic  i,  p.  18). 

THE  PERIPHERAL  NERVES. 

The  peripheral  nerves  are  divided  into  spinal  nerves  and  cranial 
nerves,  the  former  being  connected  with  the  cord,  the  latter  with  the 
brain.  Each  spinal  nerve  consists  of  two  parts — a  motor  or  efferent 
part  and  a  sensory  or  afferent  part.  Of  the  cranial  nerves  some  are 
purely  efferent,  others  purely  afferent,  while  still  others  consist  like 
the  spinal  nerves  of  both  efferent  and  afferent  fibres.  The  efferent 
fibres  of  the  spinal  nerves  are  axones  of  cell  Ijodies  situated  in  the 
anterior  horns  of  the  cord  (see  p.  404,  and  Figs.  279  and  289)  and 
axones  of  symjjathetic  ganglion  cells.  The  former  leave  the  cord  as 
separate  bundles,  which  join  to  form  the  motor  or  efferent  root.     The 


THE  NERVOUS  SYSTEM. 


381 


afferent  fibres  are  peripheral  processes  of  cell  bodies  situated  in  the 
spinal  ganglia  (p.  385  and  Figs.  279,  264).  These  leave  the  ganglion 
and  join  with  the  fibres  of  the  motor  root  to  form  the  mixed  spinal 
nerve  (Fig.  279,  /).  The  connection  of  the  ganglion  with  the  cord  is 
by  means  of  the  central  processes  of  the  spinal  ganglion  cells,  which 
enter  the  cord  as  the  posterior  root.  Among  the  afferent  fibres  of 
the   posterior  root  are  also   found,  in   some   animals,  a   few  eft'erent 


Fig.  262. — From  Transverse  Section  of  Human  Nerve  Trunk.  (Osmic  acid  fixation.) 
(Quain.)  ep,  Nerve  sheath  or  epineurium  surrounding  the  entire  nerve  and  containing 
blood-vessels  {v)  and  small  groups  of  fat  cells  (/);  per,  perifascicular  sheath  or  perineurium 
surrounding  each  bundle  or  fascicle  of  nerve  fibres;  end,  interior  of  fascicle  showing  sup- 
porting connective  tissue,  the  endoneurium. 


fibres  (Fig.  279,  c),  processes  of  cells  in  the  cord.  Some  fibres  from 
the  spinal  ganglion  and  from  the  efferent  roots  form  the  white  ramus 
communicans  to  the  sympathetic  ganglia.  Fibres  from  the  sympa- 
thetic ganglia  form  the  gray  ramus  communicans  to  the  mixed  spinal 
nerve  (Figs.  261  and  273).  For  further  details  regarding  cranial 
nerves  see  pp.  425,  426. 

The  peripheral  nerve  consists  of  nerve  fibres  supported  by  con- 
nective tissue  (Fig.  262).  Enclosing  the  entire  nerve  is  a  sheath  of 
dense  connective  tissue,  the  epineurium.  This  sends  septa  into  the 
nerve  which  divide  the  fibres  into  a  number  of  bundles  or  fascieles. 


3S2  THE  ORGANS. 

Surrounding  each  fascicle  the  connective  tissue  forms  a  fairly  distinct 
sheath,  the  perifascicular  sheath  or  perineurium.  From  the  latter, 
delicate  strands  of  connective  tissue  pass  into  the  fascicle,  separating 
the  individual  nerve  fibres.  This  constitutes  the  intrafascicular  con- 
nective tissue  or  endoneurium.  In  the  connective-tissue  layers  of  the 
perineurium  are  blood-vessels,  and  lymph  spaces  lined  with  endo- 
thelium, which  communicate  with  lymph  channels  within  the  fascicle. 
When  nerves  branch,  the  connective-tissue  sheaths  follow  the  branch- 
ings. When  the  nerve  becomes  reduced  to  a  single  fibre,  the  connect- 
ive tissue  still  remaining  constitutes  the  sheath  of  Henle.  On 
emerging  from  the  central  nervous  system,  the  root  fibres  receive  an  in- 
vestment of  connective  tissue  as  they  pass  through  the  pia  mater. 
This  is  reinforced  by  additional  connective  tissue,  as  the  nerve  passes 
through  the  dura  mater.  For  description  of  medullated  and  non- 
meduUated  nerve  fibres  see  Chap.  VL 

TECHNIC. 

Fix  a  medium-sized  nerve,  such  as  the  human  radial  or  ulnar,  by  suspending 
it,  with  a  weight  attached  to  the  lower  end,  in  formalin-Miiller's  fluid  (technic  5,  p. 
7).  Stain  transverse  sections  in  haematoxylin-picro-acid-fuchsin  (technic  3,  p.  19), 
or  hgematoxylin-eosin  (technic  i,  p.  18),  and  mount  in  balsam.  Pieces  of  nerve 
should  also  be  fixed  in  osmic  acid  imbedded,  cut,  and  mounted  without  further 
staining.     Pieces  of  fresh  nerve  may  be  teased  and  examined  without  staining. 

THE  AFFERENT  PERIPHERAL  NEURONES. 

These  consist,  as  already  stated,  of  the  bodies  and  processes  of 
the  cerebro-spinal  ganglion  cells,  probably  some  of  the  sympathetic 
ganglion  cells,  certain  cells  of  the  retina  and  certain  cells  of  the  olfactory 
mucous  membrane.  The  two  last  named  are  described  in  connection 
with  the  organs  of  special  sense. 

The  Cerebro-spinal  Ganglia. 

The  cerebro-spinal  ganglia  are  groups  of  nerve  cells  connected  with 
the  afferent  roots  of  the  cerebro-spinal  nerves.  Each  ganglion  is  sur- 
rounded by  a  connective-tissue  capsule  which  is  continuous  with  the 
perineurium  and  epineurium  of  the  peripheral  nerves.  (Fig.  261.) 
From  this  capsule  connective-tissue  trabeculae  extend  into  the  ganglion, 
forming  a  connective-tissue  framework.  Within  the  ganglion  the  nerve 
cells  are  separated  into  irregular  groups  by  strands  of  connective  tissue 


THE  NERVOUS  SYSTEM. 


383 


and  by  bundles  of  nerve  fibres.  Each  ganglion  cell  contains  a  centrally 
located  nucleus  and  a  distinct  nucleolus,  and  is  surrounded  by  a 
capsule  of  fiat,  concentrically  arranged  cells  which  are  probably  derived 
from  the  neural  plate  (p.  375)  and  are  often  called  amphicytes  or 
satellite  cells  (Fig.  265).  Stained  by  Nissl's  method  the  cytoplasm  is 
seen  to  contain  rather  small,  finely  granular  chromophilic  bodies,  which 
show  a  tendency  to  concentric  arrangement  around  the  nucleus. 
Pigmentation  is  common,  the  granules  usually  forming  a  group  in  the 


Fig.  263. — Longitudinal  Section  through  a  Spinal  Ganglion.  X  20.  (Stohr.)  a, 
Ventral  nerve  root;  b,  dorsal  nerve  root;  c,  mixed  spinal  nerve;  d,  groups  of  ganglion  cells;  e, 
nerve  fibres;/,  perineurium;  g,  fat;  h,  blood-vessel. 

vicinity  of  the  point  of  origin  of  the  main  process  of  the  cell.  The 
majority  of  the  cells  of  the  spinal  ganglia  have  one  principal  process 
which,  at  some  distance  from  the  cell  body,  divides  into  peripheral  and 
central  branches  (p.  376).  These  cells  are  usually  called  unii)oIar 
cells.  The  principal  process  usually  becomes  medullated  soon  after 
emerging  from  the  cell  capsule  (Fig.  264). 

Among  these  cells  a  number  of  forms  have  been  distinguished  by  Dogiel:  (a) 
Cells  with  only  a  principal  process.  This  process  may  pass  almost  directly 
from  the  capsule,  but  often  takes  several  turns  around  the  cell  body,  forming  a 
"glomerulus,"  before  emerging  from  the  capsule  (Fig.  264,  i  and  Fig.  265,  ,1). 
This  form  is  usually  represented  as  the  typical  cerebro-spinal  ganglion  cell,  but 
constitutes  only  a  minority  of  these  cells,  (b)  The  principal  process  gives  off  collat- 
erals. These  lie  within  the  capsule  or  are  given  off  outside  the  capsule  and  termin- 
ate in  other  parts  of  the  ganglion  and  its  covering,  either  in  terminal  arborizations 


384 


THE  ORGANS. 


or  in  terminal  enlargements  or  bulbs.  The  collaterals  may  branch.  Some  of  the 
terminations  may  be  around  the  capsules  of  other  cells.  There  may  be  one  or 
several  collaterals,  sometimes  a  number  of  very  short  intracapsular  collaterals. 
This  last  variety  of  cell  may  have  more  than  one  main  process.  (Fig.  264,  2  and  3, 
Fig.  265,  B).  (c)  Cells  with  split  processes.  Here  the  main  process  divides  into 
a  number  of  fibres  which  reunite;  this  may  be  repeated.  The  splitting  may  be 
intracapsular  or  extracapsular.  A  variation  of  this  is  where  there  are  two  to  six 
processes  from  the  cell  which  form  a  complicated  intracapsular  network,  finally 
uniting  to  form  the  single  main  process  (Fig.  264,  4  and  5  and  Fig.  265,  C  and  D). 
(d)  Cells  with  a  number  of  dendrite-like  processes  which  divide,  forming  an  intra- 


FiG.  264. — -Various  Types  of  Cells  and  Nerve  Terminations  found  in  a  Spinal 
Ganglion.  Schematized  from  Dogiel.  g.r.,  gray  ramus  communicans;  sy.c,  sympa- 
thetic cell;  w.r.,  white  ramus  communicans.  a.  Spinal  ganglion;  b,  dorsal  or  afferent 
root;  c,  ventral  or  efferent  root;  d,  sympathetic  ganglion;  g,  spinal  nerve.  For  further 
explanation  see  text  (pp.  383-385). 


capsular  network  which  finally  fuses  into  the  main  process  (Fig.  264,  6).  (e)  Cells 
whose  principal  process  divides  as  usual,  but  the  peripheral  branch  terminates  by 
arborizations  or  bulbs  in  the  ganglion  and  in  its  covering,  or  in  the  neighborhood 
of  the  dorsal  root  (Fig.  264,  7).  (f)  Bipolar  cells  (Fig.  264,  8).  (g)  Multipolar 
cells  with  a  number  of  intracapsular  dendrites  and  amain  process  (Fig.  264,  10; 
Fig.  265,  E  and  F).  (h)  Cells  with  a  principal  process  which  probably  enters  the 
dorsal  root  and  a  number  of  processes  which  may  be  dendrite-like  in  character 
but  also  become  meduUated  in  places,  and  which  branch  and  terminate  in  arbor- 
izations or  bulbs  in  various  parts  of  the  ganglion.  These  latter  apparently  collect- 
ively represent  the  peripheral  process  which  here  ends  in  the  ganglion  (Fig. 
264,  9). 

The  various  endings  in  the  ganglion  of  collaterals  and  other  processes  of  gang- 
lion cells  often  have  capsules  and  resemble  the  terminations  in  receptors  in  other 


THE  NERVOUS  SYSTEM. 


385 


parts  of  the  body  (corpuscles  of  Pacini,  end  bulbs,  etc.)  and,  together  with  their  enve- 
lopes, may  represent  the  receptors  of  the  ganglion  itself  and  of  the  connected  nerves. 
Sympathetic  fibres  enter  the  ganglion  and  form  a  plexus  within  it  from  which 
fibres  pass  and  terminate  within  the  capsules  of  the  various  ganglion  cells. 


a.f. 


Fig.  265. — Cerebro-spinal  Ganglion  Cells  and  their  Capsules.  (Cajal.)  A  (adult  man), 
Unipolar  cell  with  single  process  forming  a  glomerulus;  B  (man),  cell  with  short  process 
ending  in  intracapsular  bulb  and  main  process  giving  off  intracapsular  collateral;  C  (dog), 
"fenestrated"  cell  with  several  processes  uniting  to  form  main  process;  D  (ass),  more 
complicated  form  of  the  same;  E  (man),  cell  with  short  bulbous  dendrites;  F  (man),  cell 
with  Inilhous  dendrites  and  enveloped  with  pericellular  arborizations  (/>.a.)  of  fibres 
((/./.)  terminating  around  cell;  r,  collateral;  (/,  dendrite;  p,  principal  process;  s.p.,  short 
process.      (Cajal's  silver  slain.) 


The  peripheral  processes  of  the  cerebro-spinal  ganglion 
CELLS  arc  the  ajfcrciil  fibres  of  the  cerebro-s])inal  nerxx's  (p.  ^Si).  The 
modes  of  termination  of  these  peri|)heral  processes  are  extremclv  \-aried 


386 


THE  ORGANS. 


and  complicated.  These  peripheral  terminations  are  always  free,  in 
the  sense  that,  while  possibly  sometimes  penetrating  cells,  they  probably 
never  become  directly  continuous  with  their  protoplasm. 

In  the  skin,  and  in  those  mucous  membranes  which  are  covered  with 
squamous  epithelium,  the  nerve  fibres  lose  their  medullary  sheaths  in 
the  subepithelial  tissue,  and,  penetrating  the  epithelial  layer,  split 
up  into  minute  fibrils  which  pass  in  between  the  cells  and  terminate 
there,  often  in  little  knob-like  swellings  (Fig.  266).  In  addition  to  such 
comparatively  simple  nerve  endings,  there  are  also  found  in  the  skin 


Fig.  266. — Free  Endings  of  Afferent  Nerve  Fibres  in  Epithelium  of  Rabbit's  Bladder. 
(Retzius.)  0,  Surface  epithelium  of  bladder;  bg,  subepithelial  connective  tissue;  n,  nerve 
fibre  entering  epithelium  where  it  breaks  up  into  numerous  terminals  among  the  epithelial 
cells. 


and  mucous  membranes,  especially  where  sensation  is  most  acute, 
much  more  elaborate  terminations.  These  may  be  classified  as  (i) 
tactile  cells,  (2)  tactile  corpuscles,  and  (3)  end  bulbs. 

A  simple  tactile  cell  is  a  single  epithelial  cell,  the  centrally  di- 
rected end  of  which  is  in  contact  with  a  leaf-like  expansion  of  the 
nerve  terminal,  the  tactile  meniscus.  In  the  corpuscles  of  Grandry, 
found  in  the  skin  of  birds,  and  in  Merkel's  corpuscles,  which  occur 
in  mammalian  skin,  several  epithelial  cells  are  grouped  together  to 
receive  the  nerve  terminations.  These  are  known  as  compound  tac- 
tile cells,  the  axis  cylinder  ending  in  a  flat  tactile  disc  or  discs  between 
the  cells. 


THE  XER\-OUS  SYSTEM. 


387 


Of  the  tactile  corpuscles  (Fig.  267)  those  of  IMeissner,  which  occur 
in  the  skin  of  the  fingers  and  toes,  are  the  best  examples.  These 
corpuscles  lie  in  the  papillae  of  the  derma.  They  are  oval  bodies, 
surrounded  by  a  connective-tissue  capsule  and  composed  of  flattened 


^-^^^7^ 


'      '    v\. 


^  ?l\  \\>y'~'^Y) 


Fig.  267. 

Fig.  267. — Tactile  Corpuscle  of  Meissner,  tactile  cell  and  free  nerve  ending.  (Merkel- 
Henle.)  a,  Corpuscle  proper,  outside  of  which  is  seen  in  the  connective-tissue  capsule, 
h,  fibre  ending  on  tactile  cell;  c,  fibre  ending  freely  among  epithelial  cells. 

Fig.  268. — Taste  Bud  from  Circumvallate  Papilla  of  Tongue.  (Merkel-Henle.)  a, 
Taste  pore;  h,  nerve  fibres  entering  taste  bud  and  ending  upon  neuro-epithelial  cells.  On 
either  side  fibres  ending  freely  among  epithelial  cells. 

cells.     From  one  to  four  medullated  nerve  fibres  are  distributed  to  each 
corpuscle.     As  a  fibre  approaches  a  corpuscle,  its  neurilemma  becomes 

continuous  with  the  fibrous  capsule,  the  medullary  sheath  disappears. 


Fig.  269. — End  Bulb  from  Conjunctiva.     (Dogiel.)     a,  Medullated  nerve 
fibre,  a.xone  of  which  passes  over  into  dense  end  skein. 

and  the  filjrills  pass  in  a  spiral  manner  in  and  out  among  the  epithelial 
cells. 

Of  the  so-called  end  bulbs,  the  simplest,  which  are  found  in  the 
mucous  membrane  of  the  mouth  and  conjunctiva,  consist  of  a  central 


3S8 


THE  ORGANS. 


core  formed  by  the  usually  more  or  less  expanded  end  of  the  axis 
cylinder,  surrounded  by  a  mass  of  finely  granular,  nucleated  proto- 
plasm— the  inner  bulb — the  whole  enclosed  in  a  capsule  of  flattened 
connective-tissue  cells.  More  complicated  are  the  Pacinian  bodies 
found  in  the  subepithelial  tissues  of  the  skin  and  in  many  other  or- 
gans of  mammalia.  The  Pacinian  bodies 
(Fig.  270)  are  laminated,  elliptical  struc- 
tures which  differ  from  the  more  simple 
end  bulbs  already  described,  mainly  in  the 
greater  development  of  the  capsule.  The 
capsule  is  formed  by  a  large  number  of 
concentric  lamellse,  each  lamella  consisting 
of  connective-tissue  fibres  lined  by  a  single 
layer  of  flat  connective-tissue  cells.  The 
lamellae  are  separated  from  one  another 
by  a  clear  fluid  or  semifluid  substance.  As 
in  the  simpler  end  bulbs  there  is  a  cylin- 
drical mass  of  protoplasm  within  the  cap- 
sule known  as  the  inner  bulb.  Extending 
lengthwise  through  the  centre  of  the  inner 
bulb,  and  often  ending  in  a  knob-like  ex- 
tremity, is  the  axis  cylinder. 

In    voluntary    muscle    afferent    nerves 
thelioid    cells   lying  between    terminate    in  Pacinian    corpitsclcs,    in    end 

laminae  of   capsule;    n,   nerve      in  1       •  ^•      .     ^  1 

fibre,  consisting  of  axis  cyiin-    0^^^-^'     and    m    complicated    end    organs 

called  muscle  spindles,  or  neuromuscular 
bundles.  The  muscle  spindle  (Fig.  271)  is 
an  elongated  cylindrical  structure  within 
which  are  muscle  fibres,  connective  tissue, 
blood-vessels,  and  medullated  nerves.  The 
whole  is  enclosed  in  a  connective-tissue  sheath  which  is  pierced  at 
\'arious  points  by  nerve  fibres.  A  single  spindle  contains  several 
muscle  fibres  and  nerves.  According  to  Ruflmi,  there  are  three 
modes  of  ultimate  terminations  of  the  nerve  fil^rils  within  the  s])indles: 
one  in  which  the  end  fibrils  form  a  series  of  rings  which  encircle  the 
indi\irlual  muscle  fibre,  termed  annular  lerminalions;  a  second  in 
which  the  nerve  fibrils  wrap  around  the  muscle  fibres  in  a  spiral 
manner — spiral  lerminalions;  a  third  in  which  the  terminations  take 
the  form  of  delicate  exjjansions  on  the  muscle  fibre — arborescenl 
lerminalions.     At  the  junction   of  muscle  and  tendon  are  found  the 


Fig.  270. — Pacinian  Body  from 
Mesentery  of  Cat.  (Ranvier.) 
c,  Lamina  of  capsule;  d,  epi 


der  surrounded  by  Henle's 
sheath,  entering  Pacinian 
body;  /,  perineural  sheath; 
m,  inner  bulb;  n,  terminal 
fibre  which  breaks  up  at  a 
into  irregular  bulbous  termi- 
nal arborizations. 


THE  NERVOUS  SYSTEM. 


389 


Fig.  271. — ^Middle  Third  of  Muscle  Spindle  from  Striated  \\)luntary  Muscle  P'ibre  of  Cat. 
(From  Barker,  after  Ruffini.)     A,  rings;  5,  spirals;  J^,  arborescent  branchings. 


Fig.  272. — -Tendon  of  Muscle  of  Eye  of  O.x.  (Ciaccio.)  Two  muscle-tendon  organs 
of  Golgi,  each  showing  ring-like  and  brush-like  endings,  gli,  sheath  of  Henle;  sr, 
node  of  Ranvier. 


390  THE  ORGANS. 

elaborate   afferent    terminal    structures   known  as  the  muscle -tendon 
organs  of  Golgi  (Fig.  272). 

It  is  evident  from  the  above  that  the  nerve  terminations  are  only  stimulated 
through  the  intermediation  of  surrounding  cells  w^hich  may  form  quite  elaborate 
structures.  These  cells  constitute  the  receptors  and  probably  render  the  various 
nerve  terminations  they  envelop  more  or  less  inaccessible  to  all  but  one  par- 
ticular kind  of  stimulus.  The  above  receptors  are  scattered  throughout  head 
and  body  {general  or  common  senses)  as  distinguished  from  those  which  are  con- 
centrated into  the  organs  of  the  special  senses  (smell,  sight,  hearing,  taste)  pres- 
ent only  in  the  head  (pp.  424,  425  and  Chap.  XII).  The  various  stimuli  received 
by  them  may  give  rise  to  sensations  of  light  pressure  or  touch  (tactile  cells  and 
corpuscles?),  temperature  and  pain  (diffuse  terminations  in  epithelium  and  con- 
nective tissue?),  muscle-tendon  sense  of  movement  and  position  (muscle  spindles 
and  possibly  end  bulbs,  etc.,  in  muscles,  tendon  organs  of  Golgi?).  These  may 
be  roughly  grouped  into  general  cutaneous  or  superficial  sensation  and  deep  sen- 
sation (muscle-tendon  and  other  bodily  sensations) .  All  receptors,  both  of  general 
and  special  senses,  may  be  classified  (Sherrington)  as  those  receiving  stimuli 
from  the  external  world  (extero-ceptors,  of  superficial  sensation,  smell,  sight,  and 
hearing),  those  concerned  with  visceral  reactions  (intero-ceptors,  including  taste) 
and  those  giving  information  of  bodily  changes  {proprio-ceptors,  deep  sensation). 

The  central  processes  of  the  cerebro-spinal  ganglion 
CELLS  enter  the  central  nervous  system  as  the  fibres  of  the  afferent 
root,  the  entire  bundle  of  afferent  root  fibres  of  a  single  nerve  consisting 
of  all  the  central  processes  of  the  corresponding  ganglion.  Having 
entered  the  central  nervous  system,  the  central  processes  divide  into 
ascending  and  descending  arms,  as  already  mentioned  (p.  376). 

THE  SYMPATHETIC  GANGLIA. 

The  sympathetic  system  of  the  neck  and  trunk  consists  of  a  series 
of  vertebYal  or  chain  ganglia,  lying  ventro-lateral  to  the  vertebrae  and 
connected  by  longitudinal  cords,  and  of  gangliated  prevertebral  plexuses 
connected  with  the  vertebral  ganglia  and  also  connected  with  ill- 
defined  peripheral  ganglia  in  the  walls  of  the  viscera  {e.g.,  plexuses  of 
Auerbach  and  Meissner).  The  sympathetic  ganglia  of  the  head  are 
the  ciliary,  sphenopalatine,  otic,  and  submaxillary . 

The  peripheral  processes  of  certain  spinal  ganglion  cells  pass  via 
the  white  rami  communicantes  to  the  vertebral  ganglia  and  thence  to 
visceral  receptors.  Axones  of  splanchnic  efferent  spinal  neurones 
pass  irom  the  s[jinal  cord  via  the  ventral  roots  and  white  rami  com- 
municantes to  the  vertebral  ganglia  and  terminate  in  various  sympa- 
thetic ganglia.     The  first  thoracic  to  the  second  lumbar  spinal  nerves 


THE  NERVOUS  SYSTEM. 


391 


Smooth  muscle    Type  II 
I  \ 


Somatic  efferent 

Somatic  afferent 

Splanchnic  cerebrospinal  afferent 

Splanchnic  cerebrospinal  efferent 

Sympathetic 

-  Dorsal  root 

Spinal  ganglion 
Dorsal  ramus 


^'entral  ramus 
Blood  vessel 

Smooth  muscle 

Prevertebral  ganglion 


Afferent  sympath. neurone 


White  r.  com.  •-- 

Gray  r.  com.  •- 

Vertebral  or 
chain  gang. 


Gland 

—  Periph.  gang. 

-  -  B  lood  vessel 

Sens,  ending 

Pacinian 
corpuscle 

Fig.  273. — Diagram  of  the  Sympathetic  System  and  the  Arrangement  of  its  Neurones  in 
a  Mammal.  On  the  left  are  shown  the  typical  elements  of  a  trunk  segment  including  the 
sympathetic  system.  On  the  right  are  shown  only  the  somatic  afferent  and  efferent 
neurones  of  the  spinal  nerve.  Of  the  sympathetic  system  are  shown  the  white  and  grav 
rami,  three  ganglia  of  the  chain,  one  prevertebral  ganglion  and  one  peripheral  ganglion. 
The  symbols  used  are  explained  in  the  figure.  In  most  respects  the  diagram  follows  one 
of  Ruber's  figures.      (Johnston.) 

It  will  be  noted  that  the  sympathetic  outflow  from  any  particular  cord  segment  may 
ultimately  reach  other  segments  of  the  bodv. 


39: 


THE  ORGANS. 


are  thus  connected  with  the  sympathetic.  The  second,  third,  and 
fourth  sacral  nerves  and  visceral  branches  of  the  vagus,  glossopharyn- 
geus,  and  facialis  have  similar  connections  with  the  prevertebral  plex- 
uses. Some  cerebro-spinal  (especially  vagus)  fibres  may  pass  directly 
to  visceral  structures.  The  sympathetic  ganglia  of  the  head  are  con- 
nected with  certain  of  the  cranial  nerves  (see  p.  426). 

Some  of  the  sympathetic  cells  are  probably  afferent  but  the  ma- 
jority are  efferent  and  send  their  axones  via  the  gray  ramus  com- 


FiG.  274. — Sympathetic  Nerve  Cells  (woman  of  36  years).     (Cajal.)  A  and  B,  cells 

whose  dendrites  (b)  form  a  pericellular  plexus.   C,  cell  witli  long  dendrites,  a,  axone;  cand 

d,  terminal  fjart  of  a  dendrite.     The  capsular  cells  are  faintly  indicated.  (Cajal's  silver 
stain.) 


municans  (to  spinal  nerves),  longitudinal  cords  and  efferent  rami  to 
the  various  visceral  effectors  (see  below).  The  sympathetic  is  thus  in 
the  main  composed  of  additional  neurones  intercalated  in  the  visceral 
efferent  jjath.  The  fibres  of  the  white  rami  communicantes  are 
mostly  fine  and  medullated.  The  axones  of  the  sympathetic  cells  are 
fine  and  non-medul!atcd  or  thinly  medullated.  For  further  details 
see  Fig.  273. 

The  larger  ganglia  resemble  the  sjjinal  ganglia  in  having  a  connec- 
tive-tissue capsule  and  framework.  The  cells  are  smaller  and  often 
densely  pigmented.  Fach  cell  is  surrounded  by  a  capsule  of  cells  similar 
to  tho.se  surrounding  the  spinal  ganglion  cells.     Often  two  or  three 


THE  NER\'OUS  SYSTEM. 


393 


cells  and  their  interlocked  dendrites  are  enclosed  within  a  common 
capsule  I  Fig.  275,  A). 

The  typical  sympathetic  nerve  cell  is  a  multipolar  cell  with  short 
branching  dendrites  confined  to  the  capsule  of  the  cell  and  often  inter- 
locked with  the  dendrites  of  adjacent  cells,  forming  glomeruli.  Some- 
times a  dendrite  will  pass  some  distance  from  the  cell,  arborize,  and 


Fig.  275. — Sympathetic  Nerve-Cells  and  their  Capsules.  (Cajal).  .1,  Two-celled 
glomerulus;  B,  cell  surrounded  with  the  pericellular  terminal  arborizations  of  two  fibres 
(«./.)  passing  to  the  cell;  a,  axones;  d,  fibre,  probably  dendritic,  with  bulbous  termina- 
tion.    (Cajal's  silver  slain.) 


interlock  with  a  similar  dendritic  arborization  of  another  cell.  Another 
form  of  sympathetic  cell  has  long  slender  dendrites  often  indistinguish- 
able from  axones.  These  cells  are  more  frequent  in  the  peripheral 
ganglia.  Some  of  these  cells  have  been  considered  to  be  afferent  sym- 
pathetic cells.      (Figs.  274  and  275.) 

The    sympathetic   cells   receive   fibres   which   form   arborizations 
around  and  within  their  capsules  and  also  around  the  long  dendrites. 


394 


THE  ORGANS. 


Many  of  these  are  terminations  of  the  visceral  cerebro-spinal  efferent 

neurones  (Figs.  273  and  275,  B). 

The  axones  of  the  efferent  sympathetic  cells  terminate  in  heart 

muscle,  in  smooth  muscle  of  viscera  (viscero-motor),  of  blood-vessels 
(vaso-motor)  and  of  hairs  (pilo-motor),  and 
in  glandular  epithelia  (secretory).  In  heart 
muscle  (Fig.  276)  and  in  smooth  muscle  (Fig. 
277)  the  nerves  of  the  sympathetic  system  end 
in  fine  feltworks  of  fibres,  which  are  in  relation 
with  the  muscle  cells.  Satisfactory  dift'erentia- 
tion  between  efferent  terminals  and  aft'erent 
terminals  in  heart  and  in  smooth  muscle  has 
not  yet  been  made. 

In  organs  whose  parenchyma  is  made  up 
of  so-called  glandular  epithelium,  the  sympa- 
thetic nerves  terminate  mainly  in  free  endings 

which  lie  in  the  cement  substance  between  the  cells,  thus  coming  in 

contact  with,  though  not  penetrating,  the  epithelial  cells. 


Fig.  276. — Nerve  Endings 
on  Heart  Muscle  Cells. 
(From  Barker,  after 
Huber  and  De  Witt.) 


A. 


Fig.  277. — Nerve  Endings  on  Smooth  Muscle  Cells.     (From  Barker,  after  Huber  and  De 
Witt.)     a,  Axis  cylinder;  b,  its  termination;  n,  nucleus  of  muscle  cell. 


TECHNIC. 


(i)  Fix  spinal  and  sympathetic  ganglia  in  formalin-Miiller's  fluid  (technic  5,  p. 
7).  Stain  sections  with  haematoxylin-eosin  (technic  i,  p.  18),  or  vi^ith  ha^niatoxylin- 
picro-acid-fuchsin  (technic  3,  p.  19). 

(2)  Fix  spinal  and  sympathetic  ganglia  in  absolute  alcohol  or  in  lo-per-cent. 
formalin,  and  stain  sections  by  Nissl's  method  (technic,  p.  35). 

(3)  See  also  technic  i,  p.  399. 

(4)  Ganglia  should  also  be  prcjjarcd  by  Cajal's  silver  method,  using  the  al- 
cohol fixation  (j).  34). 


THE  NER\'OUS  SYSTEM. 


39.5 


EFFERENT  PERIPHERAL  CEREBRO-SPINAL  NEURONES. 

It  has  been  seen  that  the  bodies  of  these  neurones  lie  in  the  ventral 
part  of  the  neural  tube  where  they  form  a  part  of  the  ventral  gray 
column  in  the  cord  and  the  "motor"  nuclei  of  cranial  nerves  in  the 
segmental  brain.  The  axones  of  these  cell  bodies  emerge  as  the 
efferent  roots  and  usually  either  pass  {via  the  white  ramus  com- 
municans,  in  spinal  nerves)  to  various  sympathetic  ganglia  to  terminate 
there,  or  proceed  as  the  efferent  fibres  of  the  peripheral  nerves  to  ter- 
minate in  the  striated  voluntary  muscles  of  the  body  and  head.  In  the 


Fig. 


278. — Motor  nerve-endings  in  abdominal  muscles  of  a  rat. 
Gold  preparation.      X  170.      (.Szymonowicz). 


spinal  nerves  these  fibres  pass  beyond  the  spinal  ganglia  and  then  join 
the  afferent  fibers;  in  some  cranial  nerves  they  pass  out  with  the  afferent 
fibres.  On  their  way  to  the  muscles  the  motor  axones  may  bifurcate 
several  times,  thus  allowing  one  neurone  to  innervate  more  than  one 
muscle  fibre.  In  the  perimysium  the  nerve  fibres  undergo  further 
branching,  after  which  the  fibres  lose  their  medullary  sheaths  and 
pass  to  the  individual  muscle  fibres.  Here  each  fibre  breaks  up  into 
several  club-like  terminals  which  constitute  the  motor  cud  plate.  The 
location  of  the  end  plate,  whether  within  or  without  the  sarcolemma, 
has  not  been  determined.  As  a  rule  each  muscle  fibre  is  supplied  with  a 
single  end  plate,  though  in  large  fibres  there  may  be  several.     (Fig.  278.) 


396 


THE  ORGANS. 


THE  SPINAL  CORD. 

The  spinal  cord  encased  in  its  membranes  lies  loosely  in  the  ver- 
tebral canal,  extending  from  the  upper  border  of  the  first  cervical 
vertel^ra  to  the  middle  or  lower  border  of  the  first  lumbar  vertebra. 
It  is  cylindrical  in  shape  and  continuous  above  with  the  medulla 
oblongata,  while  below  it  terminates  in  a  slender  cord,  the  filum  ter- 
minale.  At  two  levels,  one  in  its  cervical  and  one  in  its  lumbar  region, 
the  diameter  of  the  cord  is  considerably  increased.  These  are  known, 
respectively,  as  the  cervical  and  lumbar  enlargements.  The  spinal  nerve 
roots  leave  the  cord  at  regular  intervals,  thus  indicating  a  division  of 
the  cord  into  segments,  each  segment  extending  above  and  below  its 
nerve  roots  one-half  the  distance  to  the  next  adjacent  roots.  There 
are  31  segments  corresponding  to  the  31  spinal  nerves;  8  cervical,  12 
thoracic,  5  lumbar,  5  sacral,  and  i  coccygeal. 


Origin  of  the  Fibres  which  Make  up  the  White  Matter 
of  the  Cord. 

It  has  already  been  observed  that  the  white  matter  of  the  cord  is 
composed  mainly  of  meduUated  nerve  fibres,  most  of  which  run  in  a 
longitudinal  direction.  From  the  study  of  the  neurone  it  follows  that 
each  of  these  fibres  must  be  the  axone  of  some  nerve  cell.  These 
cells,  the  medullated  axones  of  which  form  the  white  matter  of  the  cord, 
are  situated  as  follows: 


A.   Cells  oulside   the   spinal 
cord.      (Extrinsic  cells.) 


ii.  Cells  situated  in  the  fi;ray 
matter  of  the  cord.  (In- 
trinsic cells.) 


(i)  Cells  outside  the  central  nervous  system  (spinal 
ganglion  cells). 

(2)  Cells  in  other  parts  of  the  central  nervous  sys- 
tem (the  brain). 

(3)  Root  cells,  such  as  those  of  the  anterior  horn, 
whose  axones  form  the  ventral  root  (efferent 
peripheral  neurones). 

(4)  Intermediate  neurones,  whose  axones  enter  into 
formation  of  the  fibre  columns  of  the  cord 
(column  cells.) 

(5)  Cells  of  Golgi,type  II,  the  axones  of  which  ramify 
in  the  gray  matter.  (These  cells  do  not  give  rise 
to  fibres  of  the  white  matter,  but  are  conveniently 
mentioned  here  among  the  other  cord  cells.) 


THE  NER\'OUS  SYSTEM.  397 

(i)  The  Spinal  Ganglion  Cell  and  the  Origin  of  the 
Posterior  Columns. 

It  has  already  been  seen  that  the  central  processes  of  these  cells 
enter  the  cord  as  dorsal  root  fibres  and  split  into  ascending  and  descend- 
ing longitudinal  arms  composing  the  greater  part  of  the  dorsal  funic- 
ulus and  the  zone  of  Lissauer.  They  are  described  more  in  detail 
later  (pp.  413  and  414)- 


Fig.  279. — Transverse  Section  through  Spinal  Cord  and  Posterior  Root  Ganglia  of  an 
Embryo  Chick.  (\'an  Gehuchten.)  a,  Spinal  ganglion,  its  bipolar  cells  sending  their 
peripheral  processes  outward  to  become  fibres  of  the  mixed  spinal  nerve  (/),  their  central 
processes  into  the  dorsal  columns  of  the  cord  as  the  dorsal  root  fibres  (&) ;  within  the  poste- 
rior columns  these  fibres  can  be  seen  bifurcating  and  sending  collaterals  into  the  gray  matter 
of  the  posterior  columns,  one  collateral  passing  to  the  gray  matter  of  the  opposite  side. 
The  few  efferent  fibres  of  the  dorsal  root  (c)  are  disproportionately  conspicuous.  The 
large  multipolar  cells  of  the  ventral  horns  are  seen  sending  their  axones  (d)  out  of  the 
cord  as  the  ventral  root  fibres  (e)  which  join  the  peripheral  processes  of  the  spinal  ganglion 
cells  to  form  the  mixed  spinal  nerve  (/);  col,  collateral  from  axone  of  ventral  horn  cell. 
Dendrites  of  the  anterior  horn  cells  are  seen  crossing  the  median  line  in  the  anterior  com- 
missure. About  the  centre  of  the  cord  is  seen  the  central  canal;  dorsal  and  ventral  to  the 
latter  some  ependymal  cells  stretching  from  the  canal  to  the  periphery  of  the  cord. 
(Golgi  Method.) 

(2)  Cells  Situated  in  Other  Parts  of  the  Centr.4l  Nervous 
System  which  Contribute  Axones  to  the  White  Columns 
OF  the  Cord. 

These  cells  are  situated  in  the  motor  areas  of  the  cortex  of  the 
pallium,  in  the  midbrain,  cerebellum!?),  and  Mirious  ])arts  of  the 
segmental  brain.  The  axones  of  these  cells  ])ass  down  the  cord, 
forming  the  descending  fibre  tracts  of  the  cord  (]).  416).  Collaterals 
and  terminals  of  these  fibres  enter  the  gray  matter  of  the  cord  to  ter- 
minate there. 


398 


THE  ORGANS. 


(3)  Root  Cells — Motor  Cells  of  the  Anterior  Horn. 
The  course  of  the  axones  of  these  cells  has  been  described  (p.  395). 
The  bodies  are  described  on  pp.  404  and  405. 

(4)  Column  Cells. 

These  are  cells  which  lie  in  the  gray  matter  of  the  cord  and  send 
their  axones  into  the  white  columns  or  funiculi  (see  p.  403)  where 
they  either  bifurcate  or  turn  up  or  down,  becoming  longitudinal  fibres. 
Some  of  the  cells  send  their  axones  into  the  white  matter  of  the  same 

ventral 


dorsal 

Fig.  280. — Cross  Section  through  Spinal  Cord  of  Embryo  Chick  of  Eight  Days' 
Incubation.  (Cajal,  Golgi's  method.)  A,  Hecateromeric  cell  with  axone  sending  off 
side  fibril  to  gray  matter  and  then  dividing,  one  branch  passing  to  the  white  matter  of  the 
same  side,  d,  the  other  through  the  ventral  commissure  to  the  white  matter  of  the  opposite 
side,  a  and  d.  B  and  C,  Hecateromeric  cells  of  the  dorsal  gray  matter;  the  axones  divided, 
one  branch,  a,  passing  to  the  dorsal  white  columns  of  the  same  side,  the  other,  c,  through 
the  anterior  commissure  to  the  opposite  side  of  the  cord.  D,  Tautomeric  cell,  the  axones 
branching,  but  all  h)ranches  passing  to  the  gray  matter  or  white  matter  of  the  same  side  of 
the  cord.  E,  Tautomeric  cell  of  the  ventral  horn  with  axone  dividing  into  two  branches, 
a  and  d,  in  the  white  matter  of  the  same  side.  The  importance  of  the  hecateromeric 
cells  is  exaggerated  in  the  figure.  A,  B  and  C  without  side  processes  a  and  d  give  a 
good  representation  of  heteromeric  cells. 

side  of  the  cord.  These  are  known  as  tautomeric  cells  (Fig.  280,  D,  E). 
Others  send  their  axones  as  fibres  of  the  anterior  commissure  to  the 
white  matter  of  the  opposite  side  of  the  cord — heteromeric  cells.  The 
axones  of  a  few  cross  in  the  dorsal  white  commissure.  In  a  few  others 
the  axone  divides,  one  branch  going  to  the  white  matter  of  the  same 
side,  the  other  to  the  white  matter  of  the  opposite  side — hecateromeric 
cells  (Fig.  280,  A,B,C). 


THE  NER\'OUS  SYSTEM. 


399 


The  axones  of  many  of  these  cells  are  short,  constituting  the  short 
fibre  tracts  (fundamental  columns — ground  bundles)  of  the  cord  (see 
page  419;  others  are  long,  passing  up 
through  the  cord  to  the  brain  (see 
page  413).  Terminals  and  collateral 
branches  of  these  longitudinal  axones, 
especially  of  the  short  ones  are  con- 
stantly re-entering  the  gray  matter  to 
end  in  arborizations  around  the  nerve 
cells  (Fig.  281). 

(5)   Cells  of  Golgi  Type  II. 

The  axones  of  these  cells  do  not 
leave  the  gray  matter,  but  divide 
rapidly  and  terminate  in  the  gray 
matter  near  their  cells  of  origin,  some 
crossing  to  terminate  in  the  gray 
matter  of  the  opposite  side. 

TECHNIC. 

(i)  For  the  purpose  of  studying  the  spinal 
ganglion  cell  with  its  processes  and  their  rela- 
tions to  the  peripheral  nerves  and  to  the  cord, 
the  most  satisfactory  material  is  the  embryo 
chick  of  six  days'  incubation,  treated  by  the 
rapid  silver  method  of  Golgi  (technic  b,  p.  32). 
Rather  thick  (75/t)  transverse  and  longitudinal 
sections  are  made  and  mounted  in  balsam 
without  a  cover-glass.  Owing  to  the  uncer- 
tainty of  the  Golgi  reaction  several  attempts 
are  frequently  necessary  before  good  sections 
are  obtained. 

(2)  The  root  cells  of  the  anterior  horn  with 
their  axones  passing  out  of  the  cord  and  join- 
ing the  peripheral  processes  of  the  spinal 
ganglion  cells  to  form  the  spinal  nerves,  can 
usually  be  seen  in  the  transverse  sections  of 
the  six-day  embryo  chick  cord  prepared  as 
above,  technic  (i). 

(3)  For  studying  the  column  cells  of  the 
cord,  embryo  chicks  of  from  five  to  six  days' 
incubation  should  be  treated  as  in  technic  (i).     Owing  to  the  already  mentioned 
uncertainty  of  the  Golgi  reaction,  it  is  usually  necessarv  to  make  a  large  number  of 


Fig.  281. — From  Longitudinal  Section 
of  Spinal  Cord  of  Embryo  Chick. 
(Van  Gehuchten.)  .4,\\'hite  column 
of  cord;  B,  gray  matter.  The  cells 
of  the  gray  matter  (column  cells)  are 
seen  sending  their  a.xones  into  the 
white  matter,  where  they  bifurcate, 
their  ascending  and  descending  arms 
becoming  fibres  of  the  white 
column.  The  dendrites  of  these 
cells  are  seen  ramifying  in  the  gray 
matter.  To  the  left  are  seen  fibres 
(posterior  root  fibres)  entering  the 
white  matter  and  bifurcating,  the 
ascending  and  descending  arms  be- 
coming fibres  of  the  white  column. 
From  the  latter  are  seen  fibres  (col- 
laterals and  terminals)  passing  into 
the  gray  matter  and  ending  in  arbor- 
izations.    (Golgi  r^rethodj 


400  THE  ORGANS. 

sections,  mounting  only  those  which  are  satisfactorily  impregnated.  It  is  rare  for 
a  single  section  to  show  all  types  of  cells.  Some  sections  contain  tautomeric  cells, 
some  contain  heteromeric,  while  in  very  few  will  the  hecateromeric  type  be  found. 

Sections  containing  fewest  impregnated  cells  frequently  show  collaterals  to 
best  advantage.  These  are  seen  as  a  fringe  of  fine  fibers  crossing  the  boundary 
line  between  gray  matter  and  white  matter. 

(4)  The  silver  method  of  Cajal,  using  the  alcohol  fi.xation  (technic  2,  p.  34), 
mav  also  be  advantageously  used  to  display  many  of  the  above  details  of  struc- 
ture in  embryo  chicks.     It  is  also  capricious. 

"Whole  neurones  with  long  axones  obviously  cannot  be  directly  demonstrated 
in  single  sections.  To  demonstrate  these  serial  sections  and  indirect  methods 
(degeneration,  etc.)  are  used  (see  Fibre  Tracts  of  Cord). 

PRACTICAL  STUDY. 

Transverse  Section  of  Six-day  Chick  Embryo  (Technic  i,  p.  399). — Using 
a  low-power  objective,  first  locate  the  cord  and  determine  the  outlines  of  gray  mat- 
ter and  white  matter.  Observe  the  spinal  ganglia  lying  one  on  either  side  of  the  cord 
(Fig.  279,  a).  One  of  the  ganglia  will  probably  show  one  or  more  bipolar  cells,  send- 
ing one  process  toward  the  periphery,  the  other  toward  the  spinal  cord.  Note  that 
the  peripheral  process  is  joined,  beyond  the  ganglion,  by  fibres  which  come  from  the 
ventral  region  of  the  cord  (fibres  of  the  anterior  root).  In  some  specimens  the  latter 
can  be  traced  to  their  origin  in  the  cells  of  the  anterior  horn  (Fig.  279,  d).  The 
union  of  the  peripheral  processes  of  the  spinal  ganglion  cells  and  the  anterior  horn 
fibres  is  seen  to  make  up  the  mixed  spinal  nerve  (Fig.  279,/).  Observe  the  central 
processes  of  the  spinal  ganglion  cells  entering  the  dorsal  column  of  the  cord  and 
bifurcating  (Fig.  279,  b).  As  these  branches  pass  up  and  down  the  cord,  only  a 
short  portion  of  each  can  be  seen  in  a  transverse  section.  Note  the  fibres  (collaterals) 
passing  from  the  white  matter  into  the  gray  matter.  Note  in  some  of  the  sections 
a  little  round  mass  just  ventral  and  to  the  inner  side  of  the  spinal  ganglion,  in  which 
nerve  cells  may  be  seen,  and  some  fibres  passing  into  or  out  of  it.  This  represents 
the  beginning  of  the  sympathetic  system  with  its  chain  of  ganglia.  Note  the  rela- 
tion which  this  bears  to  the  spinal  cord  and  spinal  ganglia. 

In  the  same  or  other  transverse  sections  study  the  column  cells  of  the  cord, 
carefully  distinguishing  between  the  dendrites  and  axone.  This  is  not  always 
easy,  but  the  axone  can  usually  be  distinguished  as  being  more  slender,  with 
smoother  outline  and  more  uniform  size  throughout  its  course.  A.xones  may 
come  off  from  dendrites  as  well  as  from  the  cell  bodies.  At  least  one  tautomeric 
and  one  heteromeric  column  cell  should  be  found  and  studied  (Fig.  280).  Study 
also  the  collaterals  if  they  are  stained.  Remember  that  only  a  few  of  the  ele- 
ments present  are  stained  in  Golgi  preparations  and  that  there  are  apt  to  be 
pre.sent  irregular  silver  precipitates  without  any  significance.  Capillaries  often 
appear  as  a  coarse  brown-stained  meshwork. 

Study  also  any  spongioblasts  that  may  be  stained.  Those  with  nuclei  near 
the  central  canal  give  a  fair  reprei^entation  of  the  ependyma  cells  of  ihc  adult 
cord,  except  the  rcll  floes  not  usually  in  the  latter  extend  entirely  through  the 
wall  of  the  neural  lube. 


THE  XER\'OUS  SYSTEAL  401 

Longitudinal  Section  of  Six-day  Chick  Emtryo  (Technic  i,  p.  399). — 
Using  a  low-power  objective  locate  gray  matter  and  white  matter  and  identify  plane 
of  section  relative  to  transverse  section  above  described.  Note  in  the  white  matter 
longitudinally-running  fibres  from  which  branches  pass  off  into  the  gray  matter 
(Fig.  281).  Those  of  the  posterior  columns  are  the  ascending  and  descending 
branches  of  the  central  processes  of  the  spinal  ganglion  cells,  and  the  branches  pass- 
ing into  the  gray  matter  are  their  collaterals  and  terminals.  If  the  section  happens 
to  include  the  entering  fibers  of  a  posterior  root,  these  can  be  seen  branching  in  the 
posterior  columns  into  ascending  and  descending  arms  (Fig.  281).  The  longitudi- 
nal fibres  of  the  lateral  and  anterior  columns  are  axones  of  column  cells  and  of  cells 
situated  in  higher  centres  (see  pages  397  and  398).  These  also  send  collaterals  and 
terminals  into  the  gray  matter. 

General  Topography  of  the  Cord,  Cell  Groupings,  Arrangement 
of  Fibres  and  Finer  Structure. 

The  further  description  of  the  cord  is  best  combined  with  the 
practical  study  of  sections  of  the  cord,  taking  sections  through  the 
lumbar  enlargement  as  a  type. 

PRACTICAL  STUDY  OF  SECTIONS  THROUGH  LUMBAR 
ENLARGEMENT. 

General  Topography  (Figs.  282  and  283). — The  general  features  of  the  sec- 
tions can  be  best  seen  with  the  naked  eye  or  with  a  low-power  dissecting  lens. 

Notethe  shape  and  size  oi  ihe  cord,  and  that  it  is  surrounded  by  a  thin  membrane, 
the  pia  mater  spinalis;  the  deep  anterior  median  fissure,  into  which  the  pia  mater 
extends;  the  posterior  median  septum  consisting  principally  of  neuroglia,  over  which 
the  pia  mater  passes  without  entering;  and  the  postero-lateral  grooves  or  sulci  at 
the  entrance  of  the  posterior  root  fibres.  The  gray  matter  is  seen  in  the  central 
part  of  the  section  (stained  more  lightly  in  the  Weigert  preparation,  on  account  of 
the  presence  of  numerous  unstained  cell  bodies  and  dendrites)  and  arranged  some- 
what in  the  form  of  the  letter  H.  Dorsally  the  gray  matter  extends  almost  to  the 
surface  of  the  cord  as  the  dorsal  gray  columns  (posterior  horns  or  cornua).  The  ven- 
tral gray  columns  (anterior  horns)  are,  on  the  other  hand,  short  and  broad,  and  do  not 
approach  the  surface  of  the  cord.  Surrounding  the  gray  matter  is  the  while  matter 
(stained  deep  blue  in  the  Weigert  preparation).  This  is  divided  by  the  posterior 
horn  into  two  parts,  one  lying  between  the  horn  and  the  posterior  median  septum, 
the  posterior  funiculus  (dorsal  white  column);  the  other  comprising  the  remainder  of 
the  white  matter,  the  antero-lateral  funiculus  (antcro-lateral  white  column).  This 
latter  is  again  divided  by  the  anterior  horn  and  anterior  nerve  roots  into  a  lateral 
funiculus  (lateral  white  column)  and  an  anterior  jioiiculus  (ventral  white  column). 
In  the  concavity  between  the  anterior  and  posterior  horns  some  processes  of  the 
gray  matter  extend  out  into  the  white  matter  where  they  interlace  with  the  longi- 
tudinallv  running  fibres  of  the  latter  to  form  the  reticular  process  (not  well  marked 
in  the  lumbar  cord). 
26 


402 


THE  ORGANS. 


For  the  stud}'  of  further  details  the  low-power  objective  should  be  used. 

Gray  ^Iatter. — In  the  cross  portion  of  the  H  is  seen  the  central  canal,  usually 
obliterated  in  the  adult  and  represented  only  by  a  group  of  epithelial  cells.  The 
central  canal  divides  the  gray  matter  connecting  the  two  sides  of  the  cord  into  a 
ventral  gray  commissure  and  a  dorsal  gray  commissure.  Immediately  surrounding 
the  epithelial  cells  is  a  light  granular  area  composed  mainly  of  neuroglia  and  known 


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as  the  central  gelatinous  substance.  Toward  the  surface  of  the  cord  the  posterior 
horn  expands  into  a  head  or  caput,  external  to  which  is  an  area  similar  in  general 
appearance  to  that  surrounfiing  the  central  canal,  the  gelatinous  substance  of  Rolando. 
The  head  is  connected  with  the  ba.se  of  the  dorsal  horn  by  a  narrower  wec/e  or  cervix. 
External  to  the  gelatinous  sub.stance  of  Rolando  is  a  thin  zone  containing  a  plexus 
of  fine  modullatcd  fibres  (Wcigert  stain)  known  as  the  marginal  zone  or  zona  span- 


THE  NERVOUS  SYSTEAI.  403 

giosa,  and  external  to  this,  occupying  the  space  between  it  and  the  periphery,  is  a 
zone  composed  of  fine  longitudinal  medullated  fibres  rather  sparsely  arranged  and 
therefore  staining  more  lightly  with  the  Weigert  method.  This  is  the  zona  tenni- 
nalis  or  zone  of  Lissauer.  It  belongs  obviously  to  the  white  matter  of  the  cord  (see 
page  405 ).  The  portion  of  the  gray  matter  connecting  the  dorsal  and  ventral  horns 
may  be  termed  the  intermediate  or  middle  gray.  Note  the  well-defined  groups  of 
large  nerve  cells  in  the  anterior  horns  and  the  fibres  passing  out  from  the  anterior 
horns  to  the  surface  of  the  cord,  ventral  {anterior)  nerve  roots.     (Figs.  282  and  283.) 

White  Matter. — Note  the  general  appearance  of  the  white  matter  and  the 
disposition  of  the  supporting  strands  of  neurogha  tissue  (light  in  the  Weigert,  usually 
darker  in  other  stains).  The  neuroglia  is  seen  to  form  a  fairly  thick  layer  just  be- 
neath the  pia  mater  from  which  trabeculae  pass  in  among  the  fibres,  the  broadest 
strand  forming  the  posterior  median  septum.  If  the  section  has  been  cut  through  a 
dorsal  (posterior)  nerve  root,  a  strong  bundle  of  dorsal  root  fibres  can  be  seen  entering 
the  white  matter  of  the  cord  along  the  dorsal  and  mesial  side  of  the  posterior  horn. 
Just  ventral  to  the  anterior  gray  commissure  is  a  bundle  of  transversely-running 
medullated  fibres — the  anterior  white  commissure.  (Fig.  283.)  It  is  composed  of  the 
axones  of  various  heteromeric  column  cells  and  of  decussating  terminals  of  various 
fibres.  In  the  dorsal  part  of  the  dorsal  gray  commissure  are  also  a  few  fine  trans- 
versely-running medullated  nerve  fibres — the  dorsal  white  commissure.  It  consists 
of  collaterals  of  fibres  in  dorsal  funiculi  and  axones  of  heteromeric  column  cells. 

Cell  Groupings. — The  positions  and  groupings  of  the  various  cell  bodies 
should  now  be  studied.  (Nissl,  Haematoxylin-Eosin,  Cajal,  Figs.  282  and  283.) 
(For  convenience,  their  general  arrangement  throughout  the  cord  is  here  given; 
also  the  course  of  their  axones,  though  this  is  usually  only  seen  in  Golgi 
preparations.) 

(A)  Cells  of  the  Dorsal  Horn. — (a)  Marginal  cells  arranged  tangentially 
to  the  border  of  the  gelatinous  substance  of  Rolando,  (b)  Cells  in  the  gelatinous 
substance  of  Rolando,  arranged  radially.  The  Golgi  method  indicates  that  the 
axones  of  (a)  and  (b)  principally  enter  the  adjoining  lateral  column,  (c)  Large  stel- 
late cells  in  the  apex  of  the  caput,  most  of  the  axones  of  which  go  to  the  lateral 
columns,  but  some  cross  in  the  ventral  white  commissure,  (d)  A  central  group  in 
the  central  part  of  the  dorsal  cornu,  some  of  the  axones  of  which  may  cross  in  the 
ventral  commissure,  (e)  Basal  cells  in  the  base  of  the  horn  and  in  the  processus 
reticularis,  the  axones  of  which  usually  go  to  the  lateral  column  but  may  cross. 
(f)  Dorsal  (thoracic)  nucleus  or  cells  of  Clarke's  column  in  the  mesial  part  of  the  base 
of  the  dorsal  horn.  These  are  tautomeric  cells,  the  axones  of  which  form  the  dorsal 
spino-cerebellar  tract  (see  page  415).  Clarke's  column  is  mainly  confined  to  the 
dorsal  or  thoracic  cord,  but  is  also  present  in  the  first  lumbar  segment. 

(B)  Cells  of  the  Intermedlvte  Gr.a.y. — (a)  Middle  nucleus  whose  cells  may 
send  their  axones  across  in  the  ventral  commissure  or  uncrossed  to  the  lateral  column; 
(b)  various  small  cells  including  the  accessory  nucleus  near  Clarke's  column;  (c) 
intermcdio-lateral  group  which  in  parts  of  the  cord  forms  a  projection  of  the  gray 
known  as  the  lateral  horn.  These  are  probably  root  cells  whose  axones  pass  into  the 
sympathetic  system.  This  nucleus  is  more  conspicuous  in  the  thoracic  cord,  but 
extends  from  the  eighth  cervical  to  about  the  third  lumbar  segment  and  is  also  present 
in  the  sacral  cord  (especially  the  third  segment). 


404 


THE  ORGANS. 


From  the  above  it  is  seen  that  all  the  cells  of  the  dorsal  and  intermediate 
gray,  except  the  intermedio-lateral  group,  are  column  cells. 

(C)  Cells  of  the  Ventral  Horn. — These  fall  into  two  categories:  (i)  Tauto- 
meric column  cells,  sending  axones  to  the  adjoining  white  matter,  and  heteromeric 
column  cells,  the  axones  of  which  cross  in  the  ventral  commissure.  Among  the 
latter  may  be  a  well-marked  group  in  the  dorso-mesial  part  of  the  horn  (commissural 


nucleus).  {2)  Root  cells.  Two  main  divisions  may  be  distinguished:  (a)  Mesial 
group,  present  throughout  the  cord  above  the  fifth  sacral  segment  (Bruce).  This 
group  probably  innervates  the  striated  voluntary  (.somatic)  muscles  of  the  trunk. 
The  me.sial  group  is  in  part  of  the  cord  subdivided  into  a  ventro-mesial  and  dorso- 
mesial  group,  the  latter  being  present  in  the  first,  sixth  and  seventh  cervical,  thoracic 
(except  first),  and  first  lumbar  .segments,  (b)  Lateral  group,  present  in  the  cervical, 
first  thoracic,  and  lumbo-sacral  regions.     This  group  innervates  the  muscles  of  the 


THE  NERVOUS  SYSTEM.  405 

* 
extremities  and  exhibits  the  following  subdivisions:  An  antero-lateral  (C4  to  C8, 
L2  to  S2),  a  postero-lateral  (C4  to  C8,  L2  to  S3)  and  a  post-postero-lateral  (C8  to 
Thi,  Si  to  S3).  There  is  also  a  central  group  (L2  to  S2)  and  a  small  anterior  group 
(Li  to  L4).  The  exact  muscle  groups  innervated  by  these  cell  groups  respectively 
have  not  yet  been  definitely  determined.  Other  special  cell  groups  are  the  phrenic 
group  (C4),  centrally  located,  cilio-spinal  and  other  cells  (C8  to  Th2,  via  the 
sympathetic  to  dilator  pupilte  and  blood-vessels  of  head),  and  the  spinal  accessory 
(Ci  to  C6).  The  latter  is  located  laterally  and  innervates  the  sterno-mastoid  and 
trapezius  muscles. 

For  the  determination  of  the  destination  of  the  axones  of  the  efferent  root  cells 
the  method  of  studying  the  changes  in  the  cell  body  (Nissl  stain)  in  definite  lesions  of 
the  peripheral  fibres  (axonal  degeneration)  is  used. 

Arrangement  of  Fibres  (Fig.  283). — With  the  low-  and  high-power  objectives 
the  course  of  the  transverse  {i.e.,  longitudinally  cut)  nerve  fibres  should  be  carefully 
studied  in  Weigert  and  Cajal  preparations.  These  fibres  pass  from  gray  to  white 
matter  or  vice  versa,  and  are  in  general  (a)  root  fibres  entering  or  leaving  the  cord; 
(b)  either  axones  of  column  cells  in  the  gray  passing  out  into  the  white  there  to 
become  longitudinal  fibres  by  turning  or  splitting,  or  they  are  the  collaterals  and 
terminals  of  the  fibres  of  the  white  matter  entering  the  gray  to  terminate  there. 

The  arrangement  of  these  fibres  should  be  carefully- studied  in  all  parts  of  the 
section  (Weigert  and  Cajal),  taking  one  field  at  a  time.  In  the  dorsal  part  of  the 
cord,  the  dorsal  roots  can  be  seen  entering.  From  their  lateral  portion  fine  fibres 
detach  themselves  and  enter  the  zone  of  Lissauer,  the  fibres  of  which  are  largely 
composed  of  their  short  ascending  and  descending  arms.  Most  of  the  fibres  of  the 
root  passes  along  the  dorsal  and  mesial  side  of  the  dorsal  horn  forming  the  zone  oj 
entry  of  the  dorsal  roots.  By  bifurcating  (not  visible  in  the  preparation)  they  be- 
come the  longitudinal  fibres  of  the  dorsal  funiculus.  From  the  entering  root  fibres 
and  fibres  of  the  dorsal  funiculus,  bundles  of  fine  fibres  (collaterals  and  terminals) 
pass  radially  through  the  gelatinous  substance  of  Rolando  or  sweep  around  its 
mesial  side  and  enter  the  gray.  Some  of  these  terminate  in  the  gelatinous  substance 
of  Rolando  (Golgi  preparations),  some  form  part  of  the  dense  plexus  of  fibres  in 
the  caput  and  terminate  there,  others  can  be  traced  to  the  intermediate  gray  and,  in 
some  cases,  some  ("direct  reflex  collaterals")  can  be  traced  to  the  ventral  horn.  It 
will  be  noted  that  not  many  come  from  the  mesial  part  of  the  dorsal  funiculus. 
Collaterals  from  the  zone  of  Lissauer  enter  the  gelatinous  substance  of  Rolando.  In 
the  middle  part  of  the  cord  there  is  a  similar  interchange  of  fibres  between  the  plexus 
in  the  gray  and  the  adjoining  white  matter.  In  the  ventral  part  of  the  cord  a 
similar  interchange  takes  place,  but  here  besides  these  fine  fibres  are  seen  the  coarse 
fibres  of  the  ventral  roots  gathered  from  various  parts  of  the  ventral  horn  to  form 
bundles  which  leave  the  ventral  side  of  the  horn,  pass  through  the  white  matter  and 
emerge  as  the  ventral  root  fibres.  The  larger  bundles  of  fibers  in  the  ventral  horn 
separate  the  cell  groups,  but  between  individual  cells  are  seen  numerous  fine 
medullated  fibres  (principally  terminals  of  fibres  from  the  white  funiculi ).  Trace  as 
far  as  possible  the  course  of  the  fibres  of  the  ventral  and  dorsal  white  commissures. 

Finer  Structure. — Study  with  the  high  power  the  general  histological  structure 
of  the  gray  and  white  matter.  In  the  gray  matter  note  (Cajal,  Xissl,  H.-E.),  besides 
the  nerve  cells  and  their  processes,  the  neuroglia  nuclei.     Note  also  the  structure 


406 


THE  ORGANS. 


and  size  of  the  medullated  nerve  fibres  (Weigert).  In  tlie  wliite  matter  note  tl:e 
appearance  of  the  cross-cut  medullated  nerve  fibres  in  Weigert,  Cajal  and  H.-E. 
preparations.  With  the  neuroglia  stains  study  carefully  the  neuroglia  cells  and 
neuroglia  fibres,  including  the  neuroglia  zone  forming  the  margin  of  the  cord.  (Fig. 
284.)  Note  also  the  pia  mater  and  the  connective-tissue  septa  entering  the  cord 
from  the  pia  accompanied  usually  by  a  denser  aggregation  of  glia  libres.  Note 
carefully  the  number  of  neuroglia  nuclei  in  some  small  field.  Increase  in  neuroglia 
is  characteristic  of  many  pathological  conditions.  Study  the  ependyma.  (Weigert, 
Nissl,  Cajal,  glia  stain). 

Study  the  internal  structure  of  the  nerve-cells  of  various  sizes  present,  espe- 
cially the   amount   and   arrangement   of    the    chromophilic   substance    (Nissl). 


Fig.    284. — From   Transverse  Section  of  Elephant's  Cord. 
Neuroglia  Stain,     h,  c,  d  and  i,  Four  types  of  neuroglia  cells;  k, 
through  several  neuroglia  cells;  /,  leucocyte. 


(Hardesty.)       Benda's 
neuroglia  fibre  passing 


The  smallest  nerve  cells  of  the  cord  have  a  limited  amount  of  chromophilic  sub- 
stance, usually  either  in  the  form  of  perinuclear  caps  or  small  bodies  near  the 
periphery  of  the  cell.  In  the  medium  cells  more  chromophilic  bodies  are  present. 
The  cells  of  Clarke's  column  have  a  considerable  number  of  chromophilic  bodies 
arranged  near  the  periphery  of  the  cell.  The  root  cells  are  richest  in  chromophilic 
suh)stance  (for  further  details  see  Chap.  VI). 

Blood-vessels  (Fig.  285). — Study  the  arrangement  and  structure  of  the 
blood-vessels  of  the  cord  and  pia.  There  are  three  principal  longitudinal  arter- 
ies, the  anterior  spinal  artery  given  off  from  the  vertebral  arteries  near  their 
union  into  the  basilar  artery,  and  two  posterior  spinal  arteries,  given  off  from  the 
inferior  and  superior  cerebellar  arteries.  These  arteries  are  reenforced  by  small 
arteries  passing  to  the  cord  along  the  dorsal  and  ventral  roots  and  form  an 
arterial  network  in  the  pia  mater.  From  the  network  terminal  (i.  c.,  non- 
ana.stomosing)  branches  enter  the  cord,  supplying  all  parts  except  the  ventral 
horn  and  column  of  Clarke.  The  latter  are  supplied  by  branches  from  the  an- 
terior spinal  artery  which  pass  dorsally  in  the  ventral  sulcus  (sulco-commissural 
arteries)  and  enter  the  cord  alternately  to  right  and  left.     They  then  break  up 


THE  NERVOUS  SYSTEM. 


40i 


into  a  rich  capillary  network  in  the  ventral  horn,  supplying  also  a  branch  to  the 
column  of  Clarke.  The  veins  of  the  cord  also  form  a  plexus  in  the  pia  mater. 
Larger  posterior  median  and  anterior  median  veins  can  be  distinguished.  Por- 
tions of  the  above  vessels  can  be  seen,  cut  in  various  planes,  in  the  pia  and  in 
the  cord.  The  general  appearance  and  structure  of  the  blood-vessels,  including 
capillaries,  should  be  noted  in  the  various  methods  of  staining. 


Posterior  spinal  artery 


Region  supplied 
by  sulco-com- 
missural  arterv 


Column  cells 


Anterior  spinal  artery 
(giving  off  a  sulco-commissural  artery) 


Root  cells 


Fig.  285. — Schematic  transverse  section  of  Cord,  Showing  General  Distribution  of 
Blood-vessels  (left)  and  Nerve-cells  (right)  (Bing).  Root-cells;  i,  postero-lateral 
group;  2,  antero-lateral  group;  3,  antero-medial  group;  4,  central  group;  5,  postero- 
medial group.  The  broke  i  black  lines  on  the  surface  of  the  cord  are  portions  of  the 
vascular  network  in  the  pia  mater. 


Variations  in  Structure  at  Different  Levels. 

While  the  general  structure  above  described  obtains  throughout 
the  cord,  the  size  and  shape  of  the  cord,  the  size  and  shape  of  the 
gray  matter,  and  the  relative  proportion  of  gray  matter  and  while 
matter,  vary  in  different  parts  of  the  cord,  which  must  therefore  be 
separately  considered.  These  variations  are  due  to:  (i)  \'ariations 
in  the  size  of  the  nerves  entering  and  leaving,  which  cause  correspond- 
ing variations  in  the  gray  matter  which  receives  the  afferent  fibres 
and  contains  the  cells  of  origin  of  the  efferent  fibres.  Thus  the 
larger  nerves  of  the  extremities  cause  the  increase  in  size  of  the  gray 
matter  of  the  cervical  and  lumbo-sacral  cord  with  which  they  are  con- 
nected, and  also  an  increase  in  the  dorsal  funiculi.  (2)  A  gradual 
increase  in  the  white  matter  of  the  cord,  as  higher  levels  are  reached, 
due  to  an  increase  in  the  number  of  long  ascending  and  descending 
fibres  to  and  from  the  brain. 


408  THE  ORG.AJSrS. 

PRACTICAL  STUDY. 

Section  through  the  Twelfth  Thoracic  Segment  (Fig.  287). — Note  that  the 
cord  is  smaller  than  in  the  lumbar  enlargement  and  somewhat  iiattened  dorso- 
ventrally;  that  the  amount  of  gray  matter  and  white  matter  is  diminished;  that  both 
anterior  and  posterior  horns  are  more  slender,  the  anterior  horn  containing  compara- 
tively few  cells.  At  the  inner  side  and  base  of  the  posterior  horn  may  be  seen  the 
group  of  cells  known  as  Clarke's  column  (p.  403).  MeduUated  fibres  can  be  seen 
passing  from  the  dorsal  funiculus  into  Clarke's  column,  where  they  interlace  among 
the  nerve  cells.  These  fibres  are  collaterals  of  the  dorsal  root  fibres  terminating  in 
the  nucleus.  From  the  nucleus  coarser  fibres  can  be  seen  gathering  at  its  ventral 
side  and  thence  passing  outward  to  the  periphery  of  the  cord  where  they  bend 
upward  forming  the  beginning  of  the  dorsal  spino-cerebellar  tract  (see  p.  415). 

Section  through  the  Mid-thoracic  Region  (Fig.  287). — Compare  with  the 
lumbar  sections.  Xote  the  change  in  shape  and  size;  that  the  cord  is  more  nearly 
round  and  smaller;  that  while  the  reduction  in  size  affects  both  gray  matter  and 
white  matter,  it  is  the  former  that  shows  the  greater  decrease.  The  horns  are  even 
more  slender  than  in  the  twelfth  thoracic  section,  and  the  anterior  horn  contains 
still  fewer  cells.     Clarke's  column  is  present,  but  not  so  large. 

Section  through  the  Cervical  Enlargement  (Fig.  286). — Note  the  marked 
increase  in  size  of  the  cord,  which  affects  both  gray  matter  and  white  matter.  De- 
pending upon  the  exact  level  at  which  the  section  is  taken,  the  cord  may  be  nearly 
round  or  flattened  dorso-ventrally.  The  posterior  horns  remain  slender  while  the 
anterior  are  much  broader  than  the  posterior  horns.  The  reticitlar  process  is  more 
prominent  than  in  any  of  the  previous  sections.  As  in  the  lumbar  cord,  the  cell 
groups  of  the  anterior  horn  are  numerous  and  well  defined.  A  more  or  less  definite 
septum  divides  the  posterior  column  into  an  inner  part,  the  column  of  GoU,  and  an 
outer  part,  the  column  of  Burdach. 

For  further  variations  and  differences  between  the  segments  of  the  cord, 
compare  Figs.  286,  287  and  288. 

Fibre  Tracts  of  the  Cord. 

The  determination  of  the  fibre  tracts  of  the  cord  has  been  accom- 
plished principally  by  two  methods:  (i)  The  myelogenelic  method, 
which  is  based  upon  the  fact  that  the  fibres  of  difi"erent  systems  acquire 
their  myelin  sheaths  at  different  periods  of  embryonic  developm,ent. 
Thus  by  examining  cords  from  embryos  of  various  ages  and  young 
specimens  it  is  possible,  using  a  myelin  stain  {e.g.,  Weigert),  to  dis- 
tinguish different  tracts  by  the  presence  or  absence  of  myelinization  of 
their  fibres.  (2)  The  method  of  secondary  or  axonal  degeneration, 
based  ujjon  the  fact  that  a  fibre  separated  from  its  cell  undergoes 
degenerative  changes  and  ultimately  disappears  and  that  the  cell  body 
also  usually  shows  certain  changes  (see  page  124).  The  fibres  distal 
to   the   injury   can   be   distinguished   during  active   degeneration  by 


THE  NER\'OUS  SYSTEM. 


409 


C.II 


C.  Ill 


CIV 


f* 
^%j*^'. 


C.  V 


C.  VI 


C.  VII 


C.  VIII 


Fig.  2S6. — Transverse  Sections  through  the  Cervical  (II-\'III)  Segments  of  the  Cord. 
\\'eigcrt  preparations.      (Rauber-Kopsch.) 


410 


THE  ORGANS. 


Th.  I 


Th.  II 


Th.  IX 


Th.X 


Th.  XI 


Th.  XII 

Fig.  287.— Transverse  Sections  through  the  Thoracic  (I-XII)  Segments  of  the  Cord. 
Weigcrt  preparations.     (Rauber-Kopsch.) 


THE  XER\OUS  SYSTEM. 


411 


ea»^ 


L.  I 


L.  II 


L.  Ill 


L.  IV 


S.  I 


S.  II 


S.  Ill 


^^f$St^ 


S.  IV 


y   ■    ^     ri-.a 


5.  V 


Fig.  288.— Transverse  Sections  through  the  Lumbar  (I-\-)  and  Sacral  (l-Y)  Segments 
of  the  Cord.     Weigert  preparations.     (Rauber-Kopsch.) 


412 


THE  ORGANS. 


^  s- 

• 

<IJ 

^-^ 

"^ 

o~w 

©■*-. 

i^  « 

i;  ° 

■^  "^ 

^-t.- 

^^-    i 

m 

■^^ 

*// 

"S-  >- 

*^ti 

5J    fli  ti  ^qcnaj  ^^ 
H,   a,   2  C  ,, 


THE  NERVOUS  SYSTEM.  413 

applying  the  Marchi  stain  (page  31).  After  their  disappearance, 
however,  a  negative  picture  is  obtained  by  staining  the  surrounding 
normal  fibres  (Weigert).  The  changes  in  the  cell  bodies  whose  axones 
are  injured  are  distinguished  by  applying  the  Nissl  stain  (p.  35). 
Thus  if  the  cord  is  cut  at  some  particular  level,  at  any  level  above  the 
cut  all  fibres  present  which  originate  from  cells  below  the  cut  will  show 
degeneration  ("ascending"  degeneration),  while  the  cell  bodies  of  the 
cut  fibres  will  show  the  axonal  degeneration  changes.  On  the  other 
hand,  at  any  level  below  the  cut,  fibres  which  originate  from  cells  above 
the  cut  will  show  degeneration  ("descending"  degeneration),  while  the 
cell  bodies  of  these  fibres,  located  above  the  cut,  will  exhibit  axonal 
degeneration.  (3)  .4//-o/>/?3'  (von  Gudden's  method).  This  method  is 
based  upon  the  fact  that  extirpation  of  some  part  of  the  nervous  system 
in  a  young  animal  is  followed  by  an  atrophy  of  parts  in  intimate  relation 
therewith.  This  method  only  demonstrates  grosser  changes  than  the 
preceding,  but  on  the  other  hand  whole  conduction  paths  involving 
more  than  one  neurone  relay  may  show  changes.  Other  methods  are 
the  method  of  comparative  anatomy,  i.e.,  study  of  the  simpler  nervous 
systems  of  lower  forms  and  the  correlated  development  or  absence  of 
related  parts  of  the  nervous  system,  and  the  method  of  physiology,  i.e., 
study  of  effects  of  stimulation  or  extirpation  of  various  portions  of  the 
nervous  system  thereby  indirectly  demonstrating  anatomical  pathways. 

Ascending  Tracts. 

A.   Tracts  forming  parts  of  afferent  pallial  paths. 

I.  Long  Ascending  Arms  of  Dorsal  Root  Fibres.  (Posterior 
Funiculi). — The  origin  of  these  tracts — central  processes  of  the  cells 
of  the  spinal  ganglia — has  been  described  (page  390) .  The  distribution 
of  the  posterior  root  fibres  to  the  gray  matter  of  the  cord  was  noted  in 
connection  with  the  study  of  the  lumbar  enlargement  section  (page 
405).  The  general  arrangement  of  these  fibres  in  the  dorsal  funiculi 
remains  to  be  noted. 


Fig.  289 — Diagram  of  the  Tracts  of  the  Cord  (Cervical  Region).  Ascending  tracts 
are  shown  on  the  left  side,  and  descending  tracts  on  the  right.  It  will  be  noticed  that 
the  tracts  of  the  cord  are  roughly  divisible  into  three  concentric  zones:  (i)  A  zone  oc- 
cupying most  of  the  posterior  columns  and  the  peripheral  part  of  the  lateral  columns. 
This  zone  comprises  the  principal  long  ascending  tracts  (beginnings  of  afferent  supra- 
segmental  paths).  (2)  The  second  zone  lies  immediately  within  the  tirst  in  the  lateral 
columns  and  also  occupies  the  peripheral  part  of  the  anterior  columns.  It  comprises  the 
principal  long  descending  tracts  from  various  parts  of  the  brain  (terminal  portions  of  ef- 
ferent suprasegmental  paths).  (,s)  The  third  zone  borders  the  gray  matter  and  includes 
the  ground  or  fundamental  bundles  of  the  cord  (chiefly  spinal  intersegmental  fibres). 

In  the  fisrure,  for  «»,  Ddflzschni'ilschi  read  interstitial  nucleus  of  Cajal. 


4U  THE  ORGANS. 

Each  successive  dorsal  root  sends  its  fibres  into  the  cord  next  to 
the  dorsal  horn  and  therefore  to  the  outer  side  of  those  from  the  next 
root  below.  Thus  the  fibres  of  the  lower  roots  as  they  ascend  the  cord 
are  gradually  pushed  inward  toward  the  median  line  until  they  finally 
occupy  that  part  of  the  posterior  column  lying  near  the  posterior 
septum.  The  separation  of  the  posterior  column  by  a  connective-tissue 
septum  into  the  column  of  Goll  and  the  column  of  Burdach  occurs  only 
in  the  cervical  cord  (Figs.  282  and  286).  Here  the  most  median  fibres, 
i.e..  those  lying  in  the  column  of  Goll,  are  the  longest  fibres  of  the  pos- 
terior columns,  having  come  from  the  lower  spinal  ganglia,  while  the 
column  of  Burdach  (Fig.  282)  consists  of  short  and  medium  length 
fibres.  The  fibres  of  Goll's  column  end  in  the  nucleus  funicidi  gracilis 
or  nucleus  of  the  column  of  Goll  in  the  medulla  (see  p.  435  and  Fig.  297). 
Those  fibres  of  Burdach's  which  do  not  terminate  in  the  spinal  cord 
terminate  in  the  medulla  in  the  nucleus  fujiiculi  cuneati  or  nucleus  of  the 
column  of  Burdach  (p.  435  and  Fig.  297,).  The  nucleus  gracilis  and 
nucleus  cuneatus — which  will  be  seen  in  sections  of  the  medulla  (Fig. 
297) — thus  serve  as  terminal  nuclei  for  the  afferent  root  fibres  in  the 
columns  of  Goll  and  those  of  the  column  of  Burdach  which  do  not 
terminate  within  the  cord.  Inasmuch  as  many  of  the  ascending  arms 
are  short,  it  is  evident  that  only  a  fraction  of  the  dorsal  root  fibres  are 
represented  at  the  higher  levels.  Those  long  arms  which  reach  the 
medulla  constitute  the  beginning  of  one  of  the  principal  afferent 
cerebral  or  pallial  pathways.  The  axones  of  the  neurones,  whose 
bodies  are  the  nuclei  of  Goll  and  Burdach,  cross  and  form  the  tract 
known  as  the  medial  fillet  (or  lemniscus),  composing  the  second  system 
of  this  path.  The  fillet  terminates  in  the  thalamus  and  the  path  is 
completed  by  a  third  system  of  thalamo-cortical  neurones  to  the  cortex 
pallii.  This  path  is,  in  brief,  the  long  ascending  arms  of  dorsal 
roots  -f-  fillet  -f  thalamo-cortical  path,  decussating  in  the  medulla 
(Fig.  293; . 

II.  Spino-thalamic  Tract. — This  arises  from  heteromeric  cells 
lying  probaljly  principally  in  the  dorsal  horn  (groups  c  and  d,  p.  403). 
Their  axones  cross  in  the  ventral  commissure  and  reach  the  opposite 
lateral  funiculus  where  they  ascend  in  a  position  mesial  to  the  ventral 
spino-cerebellar  tract  (see  below).  This  tract  terminates  in  the 
thalamus  whence  the  path  is  completed  by  thalamo-cortical  neurones. 
The  path  is  thus:  spinal  ganglif)n  (short  arms  and  collaterals  of  dorsal 
roots)  +  spinothalamic  -F- thalamo-cortical  neurones,  three  systems  of 
neurones,     its  decussation  takes  place  in  the  cord  at  about  the  level 


THE  NER\'OUS  SYSTEM. 


415 


of  entry  of  the  dorsal  roots  involved.  Associated  with  this  system 
may  be  some  fibres  to  the  tectum  mesencephali  (spino-tectal).  (Figs. 
289,  2go  and  294). 

B.   Tracts  forming  part  of  paths  to  the  cerehellum. 

III.  Dorsal  Spino-cerebellar  Tract  {Tract  of  Flechsig.  Direct  or 
Uncrossed  Cerebellar  Tract). — This  tract  lies  along  the  dorso-lateral 
periphery  of  the  cord,  being  bounded  internally  by  the  crossed  pyrami- 
dal tract  (Fig.  282,  and  Fig.  289). 
The  fibres  of  the  direct  cerebellar 
tract  are  the  axones  of  the  cells  of 
Clarke's  column  (Figs.  289,  290 
and  294).  These  axones  cross  the 
intervening  gray  matter  and  white 
matter  of  the  same  side  (tautomeric 
column  cells)  and  turn  upward  as 
the  direct  cerebellar  tract.  In  the 
medulla  they  form  part  of  the  res- 
tiform  body  or  inferior  cerebellar 
peduncle  and  pass  to  the  cere- 
bellum. Here  they  enter  the  gray 
matter  of  the  vermis  of  the  same  or 
opposite  side,  ending  in  ramifica- 
tions among  the  nerve  cells.  Some 
fibres  either  end  in,  or  send  off 
collaterals  to,  the  cerebellar  nuclei. 
The  tract  first  appears  in  the  upper 
lumbar  cord,  and  increases  in  size 
until  the  upper  limit  of  Clarke's 
column    has    been    reached   (page 

403  J- 

As  already  noted  abo\'e,  some 
fibres  of  the  posterior  root,  or  their 
collaterals,  end  in  the  column  of 
Clarke.  This  path  is  composed 
then  of  two  systems  of  neurones, 
spinal  ganglion  cells  and  Clarke's  column  cells,  and  is  uncrossed  (with 
the  exception  that  some  fibres  are  interrupted  in  the  nucleus  lateralis 
of  the  medulla)  (Fig.  308). 

IV.  Ventral  Spino-cerebellar  Tract.— This  tract  lies  along  the 
periphery  of  the  cord,  extending  from  the  anterior  limit  of  the  direct 


Fig.  290. — Diagram  showing  Beginnings  of 
Principal  Long  Ascending  Tracts  of  Cord 
and  Termination  of  Lateral  Pyramidal 
Tract.  Each  group  of  neurones  is  repre- 
sented by  one  or  two  neurones,  d.s-c, 
Dorsal  spino-cerebellar  tract;  p,  lateral 
pyramidal  tract;  s-t.,  spino-thalamic 
tract;  v.s-c,  ventral  spino-cerebellar 
tract;  v.r.,  ventral  root. 


416  THE  ORGANS. 

cerebellar  to  about  the  exit  of  the  ventral  roots  (Fig.  282  and  Fig.  289). 
It  is  probably  formed  by  axones  whose  cell  bodies  are  scattered  through 
the  intermediate  gray  matter,  possibly  group  a  (p.  403  and  Fig.  282). 
Some  fibres  come  from  tautomeric,  others  from  heteromeric  cells,  the 
axones  of  the  latter  crossing  in  the  ventral  commissure.  The  tract 
first  appears  in  the  upper  lumbar  cord  and  naturally  increases  in  size 
as  it  passes  upward.  The  fibres  of  this  tract  also  end  in  the  vermis 
of  the  cerebellum.  They  reach  their  destination  in  the  cerebellum  by 
a  different  route,  ascending  considerably  farther  than  the  dorsal  spino- 
cerebellar fibres  and  then  turning  back  along  the  outer  side  of  the 
superior  cerebellar  peduncle  to  the  vermis.  This  path  is  thus  also  a 
two-neurone  path,  partly  crossed  and  partly  uncrossed.  The  ventral 
spino-cerebellar  and  spino-thalamic  tracts  are  sometimes  referred  to 
as  Gower's  tract.  (Figs.  294  and  308;. 

It  seems  probable  that  muscle-tendon  sense  passes  up  the  cord  by  tract  I 
(uncrossed  in  the  cord),  while  pain  and  temperature  pass  up  by  the  spino- 
thalamic tract  (crossed).  The  path  pursued  by  touch  is  more  doubtful  but  it 
may  pass  up  partly  by  tract  I  and  partly  by  ascending  arms  of  varying  lengths 
which  end  in  the  cord  around  heteromeric  column  cells  (partly  uncrossed  and 
partly  crossed  in  the  cord).  This  path  may  join  the  fillet  in  the  medulla.  It 
would  seem  probable  that  the  cerebellar  tracts  convey  sdmuli  from  muscle- 
tendon  receptors. 

Descending  Tracts. 

I,  The  Pyramidal  Tracts  {Tractus  C or tico- spinalis,  Cerehro- 
spinalis  or  Pallio-spinalis). — The  cell  bodies  of  the  neurones  whose 
axones  make  up  this  system  are  situated  in  the  cerebral  cortex  anterior 
to  the  fissure  of  Rolando  (precentral  area,  Fig.  327).  Their  axones 
converge  and  pass  downward  through  the  internal  capsule,  pes  pedun- 
culi,  pons,  and  medulla,  sending  off  fibres  to  the  efferent  nuclei  of 
the  cranial  nerves.  In  the  medulla  the  tracts  come  to  the  surface  as 
the  anterior  pyramids.  At  the  junction  of  medulla  and  cord  occurs 
what  is  known  as  the  pyramidal  decussation.  Here  most  of  the  Irbres 
of  each  tract  cross  to  the  opposite  dorso-lateral  region  of  the  cord  and 
continue  downward  as  the  crossed  pyramidal  tract.  This  lies  in  the 
dorsal  i>art  of  the  lateral  column  (Figs.  282  and  289).  It  extends 
to  the  lowermost  part  of  the  cord.  In  the  cervical  and  dorsal  regions 
it  is  separated  from  the  surface  of  the  cord  by  the  direct  cerebellar 
tract.  In  the  lumbar  region  the  latter  tract  is  no  longer  present  and 
the  crossed  pyramidal  comes  to  the  surface.     The  minority  of  the 


THE  NERVOUS  SYSTEM.  417 

fibres,  instead  of  decussating,  remain  on  the  same  side  to  pass  down 
the  cord  along  the  anterior  median  lissure  as  the  direct  pyramidal  trad, 
occupying  a  small  oval  area  adjacent  to  the  anterior  sulcus  (Fig.  289). 
It  does  not  usually  extend  below  the  middle  or  lower  dorsal  region  of 
the  cord.  As  these  tracts  descend  they  decrease  in  size  from  loss  of 
fibres  which  continually  leave  them  to  terminate  in  the  ventral  horns. 
The  fibres  of  the  crossed  tract  terminate  mainly  in  the  horn  of  the  same 
side,  while  most  of  the  fibres  of  the  direct  tract  cross  through  the  an- 
terior commissure  to  the  opposite  side  of  the  cord.  These  tracts 
are  thus  mainly  crossed  tracts,  as  the  great  majority  of  their  fibres 
cross  to  the  opposite  side  of  the  cord.  There  are,  however,  some 
homo-lateral  (uncrossed)  fibres  in  the  lateral  pyramidal  tract.  The 
tracts  are  apt  to  differ  in  size  on  the  two  sides  of  the  cord,  owing  to  the 
fact  that  the  proportion  of  fibres  which  decussate  is  not  constant. 
The  axones  terminate  in  arborizations  around  the  motor  cells  of  the 
ventral  horns.  The  pyramidal  tracts  or  pallio-spinal  system  together 
with  the  spinal  efferent  peripheral  neurone  system  constitutes  the 
pallio-spino-peripheral  efferent  conduction  path.  According  to  some 
authorities  the  pyramidal  fibres  terminate  around  cells  in  the  inter- 
mediate gray  matter  whose  axones  in  turn  terminate  around  the 
efferent  root  cells.      (Figs.  293  and  294.) 

The  pyramidal  tracts  convey  to  the  cord  the  impulses  which  result  in  volun- 
tary movements,  especially,  probably,  individual  movements  of  parts  of  the  limbs 
(foot,  hand,  finger,  etc.). 

II.  The  tecto-spinal  tract  originates  in  the  midbrain  roof, 
decussates  and  descends  to  the  cord  where  it  lies  near  the  ^■cntral 
sulcus.     Its  presence  in  the  cord  has  been  disputed.     (Fig.  320. ) 

III.  Tract  from  the  interstitial  nucleus  of  Cajal  (located  in 
the  reticular  formation  of  the  tegmentum  of  the  midbrain  cephalad 
to  the  nucleus  of  the  III  nerve). '^  It  is  uncrossed  and  lies  also  near  the 
ventral  sulcus.  Its  fibres  terminate  in  the  ventral  horn.  Some 
fibres  have  been  traced  into  the  lumljar  cord.     (Figs.  289  and  320.) 

IV.  The  Rubro-spinal  Tract  {von  Monakow's  Tract). — This 
consists  of  axones  of  tlie  red  nucleus  (nucleus  rul)er)  located  in  the 
tegmentum  of  the  midbrain.  These  axones  cross  and  descend  to 
the  cord,  being  joined  l)y  axones  of  the  other  cells  in  the  reticular  forma- 

'  The  fibres  in  question  have  been  variously  stated  to  originate  from  the  nucleus  of 
Darkschewitsch,  the  nucleus  of  the  posterior  longitudinal  fasciculus  and  the  nucleus  of 
the  posterior  commissure.  Whether  any  of  these  nuclei  is  the  same  as  the  interstitial 
nucleus  of  Cajal,  or  the  nucleus  of  van  Gehuchten  in  fishes,  is  uncertain. 


418  THE  ORGANS. 

tion  in  the  region  of  the  pons.  In  the  cord  the  tract  lies  mingled  with 
and  ventral  to  the  lateral  pyramidal  tract.  Its  fibres  terminate  in  the 
dorsal  part  of  the  ventral  horn.  This  tract  is  a  lower  link  in  a  three- 
neurone  path  from  the  cerebellum  composed  as  follows:  (a)  Cells  in 
cerebellar  cortex  to  nucleus  dentatus  in  cerebellum;  (h)  cells  in  dentatus 
via  superior  peduncle  to  the  red  nucleus;  (c)  rubro-spinal  tract  to  {d) 
efferent  peripheral  neurones  of  cord.     (Figs.  289,  294  and  308.) 

V.  Tract  from  Deiters'  Nucleus  (a  terminal  nucleus  of  the  vestib- 
ular nerve  in  the  medulla)  or  vestihulo-spinal  tract. — This  tract 
occupies  the  ventral  and  mesial  periphery  of  the  cord.  The  more 
lateral  fibres  are  uncrossed,  those  near  the  ventral  sulcus  come  from 
the  nuclei  of  both  sides.  Descending  with  these  fibres  are  probably 
axones  of  other  vestibular  nuclei,  and  of  other  nuclei  in  the  gray  reticu- 
lar formation  (reticulo-spinal  fibres)  of  the  medulla.  These  fibres  all 
terminate  in  the  ventral  horn.  Some  fibres  have  been  traced  to  the 
sacral  cord.  Deiters'  nucleus  receives  fibres  from  the  cerebellum,  and 
thus  this  tract  is  a  segment  of  a  second  efferent  cerebellar  pathway: 
{a)  Cells  in  cerebellar  cortex  to  nucleus  fastigii  in  cerebellum;  {h)  cells 
of  nucleus  fastigii  to  Deiters'  nucleus;  {c)  cells  of  Deiters'  nucleus 
to  (d)  efferent  peripheral  neurones  of  cord.  According  to  some 
authorities  some  fibres  proceed  from  cerebellum  to  cord  without 
interruption  in  Deiters'  nucleus.      (Figs.  289  and  294.) 

All  the  fibres  of  V  are  som.etimes  collectively  called  the  antero-lateral 
descending  tract  or  marginal  bundle  of  Lowenthal. 

Tract  III  and  the  mesial  part  of  V  constitute  the  major  portion  of 
the  descending  fibres  of  an  important  bundle  in  the  segmental  brain 
known  as  the  medial  longitudinal  fasciculus . 

VI.  Fasciculus  of  Thomas. — Besides  the  reticulo-spinal  fibres 
already  mentioned  are  fibres  in  the  lateral  column  which  originate  in 
the  reticular  formation  of  the  medulla  and  terminate  in  the  gray  of  the 
cer\ical  cord.     These  are  known  as  the  tract  of  Thomas.     (Fig.  289.) 

VII.  Helweg's  tract  is  a  small  triangular  bundle  of  fibres  lying 
along  the  ventro-lateral  margin  of  the  cord,  and  is  traceable  upward 
as  far  as  the  olives  (Fig.  289).  The  origin  and  destination  of  its 
fibres  are  not  definitely  known. 

VIII.  Septo-marginal  Tract. — This  is  a  small  bundle  of  fibres 
lying  next  the  ]josterior  septum.  It  appears  to  change  its  location  in 
different  levels,  e.g.,  in  the  sacral  cord  it  occupies  a  small  dorso-median 
triangle,  in  the  lumbar  region  it  forms  an  oval  bundle  (of  Flechsig)  at 
the  middle  of  the  septum  and  a  superficial  bundle,  in  the  thoracic  and 


THE  NERVOUS  SYSTEM.  419 

cervical  cord  its  fibres  are  more  scattered.  It  is  probably  composed  of 
descending  axones  of  cells  in  the  cord.      (Fig.  289). 

IX.  The  so-called  "comma"  tract  of  Schultze  is  a  small  comma- 
shaped  bundle  of  descending  fibres  lying  about  the  middle  of  the 
posterior  column  (Fig.  289).  It  is  most  prominent  in  the  dorsal  cord. 
Its  fibres  are  believed  by  some  to  be  descending  branches  of  spinal 
ganglion  cells,  by  others  to  be  descending  axones  from  cells  situated  in 
the  gray  matter  of  the  cord  (column  cells). 

In  general  the  descending  tracts  fall  into  two  categories :  (i)  descend- 
ing suprasegmental  tracts  which  originate  in  the  cortex  of  the  pallium 
(Tract  I),  or  of  the  midbrain  (Tract  II),  and  (2)  descending  inter- 
segmental tracts.  Of  the  latter  some  originate  in  nuclei  lying  in  the 
segmental  brain  (interstitial  nucleus  of  Cajal,  nucleus  ruber,  nucleus  of 
Deiters)  which  receive  efferent  suprasegmental  fibres,  and  thus  form 
links  of  descending  suprasegmental  paths.  Other  reticulo-spinal 
fibres  come  from  other  cells  in  the  gray  reticular  formation.  Other 
still  shorter  tracts  (spino-spinal),  from  cells  in  the  cord,  form  the  de- 
scending fibres  in  the  ground  bundles  (see  below).  Tracts  \TII  and 
possibly  IX,  are  in  this  category. 

Many  tracts  contain  fibres  proceeding  in  a  direction  opposite  to  that  of  most 
of  the  fibres. 

Fundamental  Columns  or  Ground  Bundles. 
The  ascending  and  descending  tracts  above  described  are  known 
as  the  long-fibre  tracts  of  the  cord.  If  the  area  which  these  tracts 
occupy  be  subtracted  from  the  total  area  of  white  matter,  it  is  seen  that 
a  considerable  area  still  remains  unaccounted  for.  This  area  is 
especially  large  in  the  antero-lateral  region,  and  extends  up  along  the 
lateral  side  of  the  posterior  horn  between  the  latter  and  the  crossed 
pyramidal  tract  (Figs.  282  and  289).  A  small  area  in  the  posterior 
column  just  dorsal  to  the  posterior  commissure,  and  extending  up  a 
short  distance  along  the  medial  aspect  of  the  horn,  should  also  be 
included.  These  areas  are  occupied  by  the  fundamental  columns  or 
short-fibre  (spino-spinal  or  proprio-spinal)  systems  of  the  cord.  The 
fibres  serve  as  longitudinal  commissural  fibres  to  bring  the  dift"erent 
segments  of  the  cord  into  communication  (Fig.  292).  The  shorter 
fibres  lie  nearest  the  gray  matter  and  link  together  adjacent  segments. 
The  longer  fibres  lie  farther  from  the  gray  matter  and  continue  through 
several  segments.  The  origin  of  these  fibres  as  axones  of  cells  of  the 
gray  matter,  and  the  manner  in  which  they  re-enter  the  gray  matter  as 
terminals  and  collaterals  have  been  considered  (pp.  39S  and  399). 


420 


THE  ORGANS. 


The  fact,  alluded  to  above,  that  the  shorter  fibres  lie  nearest,  or 
mingled  with  the  gray  is,  in  a  general  way,  true  throughout  the  central 
nervous  system.  A  result  of  this  in  the  cord  is  the  superficial  position 
of  many  of  the  longest  tracts. 

Attention  has  already  been  called  to  the  concept  of  neural  arcs  which 
may  traverse  the  cord  or  both  cord  and  suprasegmental  structures 
(page  378). 

It  must  be  kept  in  mind  that  there  are  probably  no  isolated  neural  arcs  and 
that  every  neural  reaction  involving  any  given  arc  always  influences  and  is  in- 
fluenced by  other  parts  of  the  nervous  system. 

Receptor 


Effector 
Fig.  291 — -Diagram  illustrating  a  Two-neurone  Spinal  Reflex  .\rc.      Groups  of  neu- 
rones are  represented  by  one  neurone,     gg,  Spinal  ganglion.     (Van  Gehuchten). 

From  the  neurones  thus  far  studied  and  the  tracts  which  their 
axones  form,  the  following  neural  arcs  may  be  constructed: 

(i)  A  Two-neurone  Spinal  Reflex  Arc  (Fig.  291). — {a)  Peripheral 
afferent  neurones;  their  peripheral  processes  and  receptor,  the  spinal 
ganglion  cells,  their  central  processes  with  collaterals  terminating 
around  motor  cells  of  anterior  horn;  (/;)  peripheral  efferent  neurones, 
i.e.,  motor  cells  of  anterior  horn  with  axones  passing  to  effector.  Such 
a  two-neurone  reflex  arc  is  chiefly  uncrossed  and  in  most  cases  in- 
volves only  one  segment  or  closely  adjacent  segments.  As  it  involves 
only  one  synapsis  (see  chapter  VT)  fin  the  ventral  gray)  it  is  some- 
times termed  a  monosynaptic  arc. 


THE  XERVOUS  SYSTEM. 


421 


(2)  .4  Three-neurone  Spinal  Reflex  Arc  (Fig.  292). — (a)  Peripheral 
afferent  neurmies  as  in  (i),  but  terminating  around  column  cells  of  the 
cord.  1/))  Cord  neurones  (column  cells) — axones  in  the  fundamental 
columns  with  collaterals  and  terminals  to  anterior  horn  cells  of  different 
levels.  \c)  Peripheral  efferent  neurones  as  in  the  two-neurone  reflex. 
Such  a  three-neurone  or  disynaptic   reflex 

arc  may  involve  segments  above  or  below 
the  segment  of  entrance  of  the  stimulus 
and  is  uncrossed  or  crossed  according  as 
the  cord  neurones  are  tautomeric  or 
heteromeric. 

The    independence    of    the   cord   as  a  reflex 
mechanism  is  much  diminished  in  man. 

(3)  -4  cerebellar  Arc  may  be  constituted 
as  follows:  [a)  Peripheral  afferent  neurones 
to  {h)  column  cells  in  cord  {e.g.,  Clarke's 
column)  via  spino-cerebellar  tracts  to  cere-  y. 
bellar  cortex;  (c)  various  associative  cortical 
neurones;  [d)  axones  of  cortical  cells  to 
{e)  dentate  nucleus  the  axones  of  which 
(superior  peduncle)  pass  to  (/)  nucleus 
ruber  via  rubro-spinal  tract  to  [g)  efferent  p; 
peripheral  neurones  in  cord.  Another  arc 
would  consist  of  {a),  {h)  and  (c)  the  same, 
{d)  cerebellar  cortex  to  nucleus  fastigii  in 
cerebellum  to  {e)  nucleus  of  Deiters  to  (/) 
efferent  peripheral  neurones  to  effector 
(Figs.  294  and  308). 

(4)  -4  Cerebral  or  Pallial  Arc:  {a)  Peripheral  afferent  neurones,  via 
long  ascending  arms  to  (b)  nucleus  gracilis  or  cuneatus,  thence  as 
medial  lemniscus  to  (c)  thalamus  to  cortex  pallii;  {d)  associative 
neurones  of  cortex;  (e)  cortical  precentral  neurones  via  pyramid  to 
(/)  efferent  peripheral  neurones  to  effector.  Another  arc  would  invoh-e 
the  spino-thalamic  tract  instead  of  the  lemniscus.      (Figs.  293  and  20^4.) 

Similar  arcs  may  include  eft'erent  sympathetic  neurones. 

TECHNIC. 

fi)  Carefully  remove  the  cord  (human  if  possible;  if  not,  that  of  a  large  dog) 
with  its  membranes,  cut  into  two  or  three  pieces  if  necessary,  and  lay  on  sheet 
cork.     Slit  the  dura  along  one  side  of  the  cord,  lay  the  folds  back,  and  pin  the 


292. — Diagram  illustrating 
Three-neurone  Spinal  Refle.x 
.Arcs  of  one  segment  and  more 
than  one  segment.  Groups  of 
neurones  are  represented  by 
one  neurone,  g.  Spinal  gang- 
lion cells;  h.c.c,  heteromeric 
column  cell:  t.c.c,  tautomeric 
column  cell;  x'.r.,  ventral  root. 


422 


THE  ORGANS. 


dura  to  the  cork.  Care  must  be  taken  to  leave  the  dura  very  loose,  otherwise  it 
will  flatten  the  cord  as  it  shrinks  in  hardening.  With  a  sharp  razor  now  cut  the 
cord,  but  not  the  dura,  into  segments  about  i  cm.  thick.    Fix  in  Orth's  fluid  (p.  7). 

Pieces  of  the  cord  may  be 
cut  out  as  wanted  and  em- 
bedded in  celloidin.  Sec- 
tions should  be  cut  about 
15K  in  thickness. 

(2)  For  the  study  of  the 
general  internal  structure  of 
the  cord,  stain  a  section 
through  the  lumbar  enlarge- 
ment of  a  cord  prepared 
according  to  the  preceding 
technic  (i)  in  haematoxylin- 
picro-acid-fuchsin  (technic 
3,  p.  19)  and  another  section 
through  the  same  level  in 
Weigert's  haematoxylin 
(technic  p.  29).  Mount 
both  in  balsam.  For  Weigert 
staining,  material  fixed  in 
formalin  or  in  Orth's  fluid 
should  be  further  hardened 
in  Miiller's  fluid  for  at  least 
a  month,  changing  the  fluid 
frequently  at  first  to  remove 
the  formalin.  Mallory's  glia 
stain  should  also  be  used 
with  material  fixed  in 
Zenker's  fluid  (technic,  p. 
27).  The  silver  method 
of  Cajal  (alcohol-fixation) 
should  also  be  used  (technic, 
p.  34)  and  that  of  Nissl. 

(3)  From  a  cord  prepared 
according  to  technic  i,  re- 
move small  segments  from 
each  of  the  following  levels: 
(i)  the  twelfth  dorsal,  (2) 
the  mid-dorsal,  and  (3)  the 
cervical  enlargement.  The 
segments  are  embedded  in 
celloidin,  sections  cut  15  to 
20/'.  thick,  stained  by 
Weigert's  method  (page 
29),     and     mounted    in 


Fig. 


293- 


THE  XER\-OUS  SYSTEM.  423 

balsam.      Medullated   sheaths   alone   are   stained    by   this    method   and   appear 
dark    blue    or   black. 

(4)  A  human  cord  from  a  case  in  which  death  has  occurred  some  time  after 
fracture  of  the  vertebrae  with  resulting  crushing  of  the  cord,  furnishes  valuable  but 
of  course  rarely  available  material.  If  death  occur  within  a  few  weeks  after  the 
injury,  the  method  of  Marchi  should  be  used;  if  after  several  weeks,  the  method  of 
Weigert  (page  29).  The  picture  in  the  cord  is  dependent  upon  the  fact  that  axones 
cut  off  from  their  cells  of  origin  degenerate  and  disappear.  After  a  complete 
transverse  lesion  of  the  cord,  therefore,  all  ascending  tracts  are  found  degenerated 
above  the  lesion,  all  descending  tracts  below  the  lesion.  The  method  of  ^larchi 
gives  a  positive  picture  of  osmic-acid-stained  degenerated  myelin  in  the  affected 
tracts.  The  method  of  Weigert  gives  a  negative  picture,  the  neuroglia  tissue  which 
has  replaced  the  degenerated  tracts  being  unstained  in  contrast  with  the  normal 
tracts,  the  myelin  sheaths  of  whose  fibers  stain,  as  usual,  dark  blue  or  black. 

(5)  Human  cords  from  cases  which  have  lived  some  time  after  the  destruction 
of  the  motor  cortex,  or  after  interruption  of  the  motor  tract  in  any  part  of  its  course, 
may  also  be  used  for  studying  the  descending  fibre  tracts. 

(6)  The  cord  of  an  animal  may  be  cut  or  crushed,  the  animal  kept  alive  for 
from  two  weeks  to  several  months,  and  the  cord  then  treated  as  in  technic  (4).  The 
most  satisfactory  animal  material  may  be  obtained  from  a  large  dog  by  cutting 
the  cord  half-way  across,  the  danger  of  too  early  death  from  shock  or  complica- 
tions being  much  less  than  after  complete  section. 


Fig.  293. — Diagram  showing  the  Most  Important  Direct  Paths  which  an  Impulse 
follows  in  passing  from  a  Receptor  (5)  to  the  Cerebral  Cortex  and  from  the  latter  back  to 
an  Effector  (M)  {e.g.,  muscle),  also  some  of  the  cranial-nerve  connections  with  the  cerebral 
cortex.  Groups  of  neurones  are  represented  by  one  or  several  individual  neurones.  A, 
Sensory  cortex:  B,  motor  cortex;  C,  level  of  third  nerve  nucleus:  D.  level  of  sixth  and 
seventh  nerve  nuclei;  E,  level  of  sensory  decussation:  F,  level  of  pyramidal  decussation;  6', 
spinal  cord. 

From  Periphery  to  Cortex. 

jVeurone  No.  i. — The  Peripheral  afferent  Neurone:  i,  Spinal,  cell  bodies  in  spinal 
ganglia:  receptor,  S,  peripheral  arm  of  spinal  ganglion  cell:  central  arm  of  spinal  ganglion 
cell  as  fibre  of  dorsal  root  to  column  of  GoU  or  of  Burdach,  thence  to  nucleus  of  one  of 
these  columns  in  the  medulla.  Tj,  Cranial  (example,  fifth  cranial  nerve,  trigeminus:  cell 
bodies  in  Gasserian  ganglion):  receptor:  peripheral  arm  of  Gasserian  ganglion  cell:  central 
arm  of  Gasserian  ganglion  cell  to  medulla  as  aff'erent  root  of  fifth  nerve,  thence  to  terminal 
nuclei  in  medulla. 

Neurone  No.  2. —  2,  Spinal  connection — cell  body  in  nucleus  of  Goll  or  of  Burdach :  axone 
passing  as  fibre  of  fillet  to  thalamus.  ]'.,,  Cranial  nerve  connection  (trigeminal),  cell  body 
in  one  of  trigeminal  nuclei  in  medulla,  axone  as  fibre  of  secondary  trigeminal  tract  to 
thalamus. 

Neurone  No.  3. — 3,  Cell  body  in  thalamus,  a.xone  passing  through  internal  capsule  to 
termination  in  cortex.     (Various  association  neurones  in  cortex  omitted.) 

From  Cortex  to  Periphery. 

Neurone  No.  4. — 4,  Cell  body  in  motor  cerebral  cortex:  axone  through  internal  capsule 
and  pes  to  (a)  motor  nuclei  of  cranial  nerves,  (b)  by  means  of  pyramidal  tracts  to  ventral 
gray  of  spinal  cord. 

Neurone  No.  5. — 5,  Spinal,  cell  body  in  ventral  gray  of  cord:  axone  as  motor  fibre  of 
ventral  root  through  mi.xed  spinal  nerve  to  effector  (muscle). 

Neurone  No.  5. — Cranial — 1'-,  Cell  body  in  motor  nucleus  of  trigeminus:  axone  passing 
to  muscle  as  motor  fibre  of  fifth  nerve. 

III3,  Peripheral  efferent  neurone  of  third  nerve — oculomotor.  1'/-,  Peripheral 
efferent  neurone  of  sixth  nerve — abducens.  1'//-,  Peripheral  efferent  neurone  of  seventh 
nerve — facial.     NII^,  Peripheral  efferent  neurone  of  twelfth  nerve — hypoglossal. 


424  THE  ORGANS. 

(7)  The  cord  of  a  human  foetus  from  the  sixth  month  to  term  furnishes  good 
material  for  the  study  of  the  anterior  and  posterior  root  fibres,  the  plexus  of  fine 
fibres  in  the  gray  matter,  the  groupings  of  the  anterior  horn  cells,  etc.  The  pyram- 
idal tracts  are  at  this  age  non-meduUated  and  are  consequently  unstained  in  Wei- 
gert  preparations.     The  Weigert-Pal  method  gives  the  best  results. 

(8)  For  the  study  of  the  course  of  the  posterior  root  fibres  within  the  cord, 
cut  anv  desired  number  of  posterior  roots  between  the  ganglia  and  the  cord  and 
treat  material  by  the  Marchi  or  the  Weigert  method,  according  to  the  time  elapsed 
between  the  operation  and  the  death  of  the  animal. 

BRAIN. 

General  Structure. 

The  principal  peculiarities  of  the  brain  as  distinguished  from  the 
cord  depend  upon  two  factors:  certain  peculiarities  of  the  receptors 
and  effectors  of  the  head  and  the  development  of  higher  coordinating 
apparatus  in  the  central  nervous  system  of  the  head. 

Besides  the  receptors  of  the  general  senses  (p.  390),  there  are  in  the 
head  the  highly  specialized  receptors  of  smell,  sight,  hearing  and  position 
(semi-circular  canals),  which  are  respectively  concentrated  into  certain 
localities  and  form,  together  with  certain  accessory  structures,  the  organs 
known  as  the  nose,  eye  and  ear.  Each  of  these  groups  of  receptors 
has  its  own  special  connection  with  the  brain  (nerves  I,  II  and  VIII) 
and  its  own  paths  within  the  latter  (see  below).  The  special  receptors 
of  taste  show  a  less  degree  of  aggregation  into  an  organ  and,  together 
with  other  visceral  receptors,  are  innervated  by  afferent  portions  of  a 
group  of  nerves  (VII,  IX  and  X)  which  have  a  common  continuation 
within  the  brain.  The  remaining  somatic  receptors  of  the  general 
senses,  scattered  over  the  anterior  part  of  the  head,  are  innervated  by 
one  nerve  (V)  having  its  own  central  continuations.  The  striated 
voluntary  muscles  of  the  head  fall  into  four  groups;  those  of  the  eye, 
of  the  mouth,  of  the  face,  pharynx  and  larynx  (modified  branchial 
musculature)  and  of  the  tongue.  The  oral  and  branchial  muscula- 
tures are  usually  regarded  as  visceral  and  those  of  the  eye  and  tongue 
as  somatic,  a  distinction  shown  by  differences  of  grouping  in  the  brain 
of  their  efferent  peripheral  neurones.  The  nose  and  ear  have  practic- 
ally no  N'oluntary  motor  apparatus. 

The  higher  coordinating  apparatus  or  suprasegmcntal  structures 
(p-  377J  ^-"f  ^^^  brain  arc  essentially  expansions  of  the  dorsal  walls  of 
parts  of  the  brain  having  manifold  connections  with  the  rest  of  the 
nervous  system  which  are  complexly  interrelated  by  enormous  num- 


THE  NERVOUS  SYSTEM.  425 

bers  of  association  neurones.  The  presence  of  these  latter  has  prob- 
ably necessitated  the  extensive  layers  of  externally  placed  neurone 
bodies  (cortex)  characteristic  of  suprasegmental  structures. 

The  structure  of  the  basal  part  of  the  brain,  connected  with  the 
cranial  nerves  (segmental  brain,  p.  377),  is  affected  by  both  the  pecu- 
liarities of  peripheral  structures  mentioned  above  and  by  the  presence 
of  bundles  of  fibres  and  masses  of  gray  forming  portions  of  paths  to 
and  from  suprasegmental  structures  (see  below). 

The  following  summary  embodies  the  resulting  general  structural 
features  of  the  brain: 

Segmental  Brain  and  Nerves. 

Afferent  Peripheral  (Segmental)  Neurones. — (i)  Visceral 
group  comprising  nerves  VII  (geniculate  ganglion),  IX  (superior  and 
petrosal  ganglia)  and  X  (jugular  and  nodose  ganglia).  The  nerves 
of  taste  probably  belong  entirely  to  this  group.  The  peripheral 
arms  of  these  ganglia  innervate  visceral  receptors  and  the  central 
arms  form  a  descending  tract  in  the  medulla,  the  fasciculus  solitarius 
which  has  its  terminal  nucleus  giving  rise  to  secondary  tracts. 

(2)  General  Somatic  Group  (common  sensibility). — Semilunar  gang- 
lion of  \ .  Peripheral  arms  to  skin  of  anterior  part  of  head,  to  mouth 
and  probably  to  muscle  tendon  receptors.  Central  arms  form  de- 
scending tract  in  medulla,  the  radix  spinalis  \\  Terminal  nucleus 
the  continuation  in  medulla  of  dorsal  horn.  Secondary  tract  to 
thalamus  and  thence  to  cortex  cerebri. 

(3)  Semicircular  Canal  Group. — Ganglion  of  Scarpa  of  \'III. 
Peripheral  arms  to  semicircular  canals.  Central  arms  constituting 
vestibular  portion  of  VIII,  forming  descending  tracts  in  medulla  and 
terminating  in  several  vestibular  terminal  nuclei  (including  Deiters). 

(4)  Acoustic  Group. — Ganglion  spirale  of  VIII.  Peripheral  arms 
to  cochlea.  Central  arms  forming  cochlear  part  of  \'III  and  termi- 
nating in  medulla  in  various  nuclei  with  secondary  tract  (lateral  lillet) 
to  midbrain.  Thence  by  third  system  of  neurones  to  medial  geniculate 
body  and  by  fourth  system  of  neurones  to  cortex  cerebri. 

(5)  Visual  Group. — Ganglion  in  retina.  Second  neurone  system 
beginning  in  retina  and  forming  the  optic  tract  (optic  "nerve")  to 
lateral  geniculate  body  and  by  third  neurone  system  to  cortex  cerebri. 

(6)  Olfactory  Group. — "Ganglion"  cells  in  olfactory  mucous 
membrane  forming  olfactorv  nerve  (fila  olfactoria).     Secondarv  tracts 


426  THE  ORGANS. 

from  olfactory  bulb  (and  tertiary  tracts)  to  parts  of  diencephalon  and 
hippocampus. 

Efferent  Peripheral  (Segmental)  Neurones. — (i)  Visceral. — 
(a)  Bodies  more  laterally  placed  in  gray  matter  of  hindbrain. 
Axones  to  striated  voluntary  muscles  of  jaw  (V),  face  (VII),  pharynx 
and  larynx  (IX  and  X).  {b)  Bodies  more  deeply  placed  in  gray  of 
mid-  and  hindbrain.  Axones  to  glands,  smooth  and  heart  muscle, 
either  directly  or  via  sympathetic  ganglia  of  head  and  body. 

(2)  Somatic. — Bodies  located  near  median  line  in  gray  matter  of 
hindbrain  (XII  and  VI),  and  midbrain  (IV  and  III),  to  muscles  of 
tongue  (XII)  and  eye  (VI,  IV  and  III).  Nerve  III  also  contains 
neurones  whose  axones  pass  to  sympathetic  ganglia  (ciliary). 

(3)  Sympathetic. — Bodies  compose  the  sympathetic  ganglia  of  the 
head  (ciliary,  sphenopalatine,  submaxillary  and  otic).  These  ganglia 
are  connected  with  afferent  and  efferent  portions  of  cranial  nerves 
(III,  V,  VII,  IX  and  X),  in  a  manner  similar  to  the  connections 
between  sympathetic  ganglia  of  body  and  spinal  nerves.  They  are 
also  connected  with  sympathetic  fibres  from  the  body. 

Intersegmental  Neurones. — These  are  represented  principally 
by  the  gray  reticular  formation  of  the  hindbrain  and  midbrain  and 
long  descending  tracts  external  to  it.  The  gray  reticular  formation 
is  composed  of  neurone  bodies  and  short  intersegmental  tracts  inter- 
mingled. Among  the  former  are  certain  well  differentiated  nuclei  {e.g., 
nucleus  ruber,  nucleus  of  Deiters  and  interstitial  nucleus  of  Cajal)  the 
axones  of  which  form  long,  principally  descending,  intersegmental 
tracts  external  to  the  gray  reticular  formation.  Other  cells  in  the 
gray  reticular  formation  form  the  shorter  tracts  within  it.  The 
reticular  formation  may  also  contain  the  motor  nuclei  of  the  cranial 
nerves  and  is  traversed  by  various  fibers  passing  to  tracts  and  by 
terminals  from  tracts. 

Afferent  and  Efferent  Suprasegmental  Patlis. — The  afferent 
paths  consist  of  the  ascending  tracts  and  nuclei  already  mentioned 
(spino-cerebellar,  nuclei  gracilis  and  cuneatus  and  medial  lemniscus, 
terminal  nuclei  of  the  afferent  cranial  nerves  and  their  secondary 
tracts  and  further  continuations).  The  tracts  occujjy,  in  general, 
positions  external  to  the  reticular  formation  and  long  intersegmental 
tracts.  The  efferent  suprasegmental  paths  consist  either  of  descending 
suprasegmental  tracts  which  proceed  without  interruption  to  the 
efferent  ]jeri]jhcral  neurones,  or  of  descending  suprasegmental  and 
short  or  long  intersegmental  tracts  in  whose  nuclei  the  suprasegmental 


THE  NERVOUS  SYSTEM.  427 

tracts  terminate  and  which  in  turn  terminate  around  the  efferent 
peripheral  neurones.  The  large  descending  tracts  from  the  pallium 
markedly  affect  the  configuration  of  the  brain.  There  are  two  such 
principal  descending  pallial  paths;  one  to  the  nuclei  of  the  pons 
VaroHi  and  thence  across  to  the  opposite  cerebellar  hemisphere  and 
one  continuing  down  to  the  medulla  and  cord  as  the  pyramids.  These 
two  paths  are  added  ventrally  to  the  segmental  and  intersegmenta- 
apparatus  and  form  the  pes  pedunculi  (added  ventrally  to  the  tegmenl 
tum  of  the  midbrain),  the  pons  Varolii  (ventral  to  the  tegmentum  of 
part  of  the  midbrain,  to  the  isthmus  and  part  of  the  hindbrain)  and 
the  pyramids  (ventral  to  the  hindbrain). 

SUPRASEGMENTAL  STRUCTURES. 

These  are  the  pallium  or  cerebral  hemispheres,  the  corpora  quad- 
rigemina  and  the  cerebellum.  They  consist  essentially  of  the  end- 
ings and  beginnings  of  their  respective  afferent  and  efferent  paths  and 
of  their  own  association  neurones,  the  bodies  of  which  lie  in  their 
respective  cortices. 

The  corpora  quadrigemina  are  relatively  of  much  less  importance  in  the 
human  brain. 

In  accordance  with  the  above  there  are  usually  to  be  distinguished 
in  transverse  sections  of  the  brain  at  various  levels  the  following: 

A.  Peripheral  {segmental)  neurones,  (i)  Efferent  ("motor"  nuclei 
and  root  fibres). 

(2)  Central  continuations  of  afferent  neurones  (afferent  roots),  {a) 
Those  entering  at  and  therefore  belonging  to  the  segment  involved. 
{b)  Those  entering  above  or  below  the  segment  and  represented  in  the 
segment  by  descending  or  ascending  (overlapping)  tracts. 

B.  Terminal  nuclei  of  (2)  and  the  secondary  tracts  originating  from 
them.     These  may  fall  under  category  C  or  D  (below). 

C.  Intersegmental  nuclei  and  tracts  oi  the  segmental  brain,  consist- 
ing principally  of  the  gray  reticular  formation  and  long  descending 
tracts  (arrangement  much  modified  in  forebrain). 

D.  Nuclei  and  tracts  forming  a/fcrcnt  and  efferent  suprascgmental 
paths. 

E.  Suprascgmental  structures  (not  present  in  man}'  transections). 
The  aft'erent  paths  include  some  of  the  nuclei  and  tracts  under  B, 

and  their  continuations,  and  the  efferent  include  some  of  the  longer 
systems  under  C,  together  with  cft"crcnt  su]irasegmcntal  tracts  to  them. 


428 


THE  ORGANS. 


^     S_P_H 


SP.  c;anc,  cell 


Fig.  294. 


THE  NERVOUS  SYSTEM.  42!) 

The  general  histology  of  the  brain  is  similar  to  that  of  the  cord. 
The  largest  nerve-cells  (large  cells  of  efferent  or  motor  nuclei,  cells  in 
motor  cerebral  cortex  and  certain  cells  in  the  reticular  formation) 
usually  present  a  chromophilic  substance  similar  in  arrangement,  etc.. 
to  the  efferent  nerve  cells  of  the  cord.  The  Purkinje  cells,  however, 
differ  from  these  (see  cerebellum).  The  chromophilic  substance  of 
medium  and  small  cells  presents  an  appearance  in  general  similar  to 
corresponding  cells  of  the  cord.  Many  minor  differences  may,  however, 
obtain  between  various  neurone  groups.  The  neuroglia  cells  and 
fibres  also  present  the  same  general  characteristics  as  those  in  the 
cord,  with  variations  peculiar  to  certain  localities  (e.g.,  parts  of  the 
cerebellum). 

Hindbrain  or  Rhombencephalon. 

This  includes  the  medulla,  cerebellum,  and  part  of  the  tegm.entum 
and  pons.  Its  peripheral  nerves  are  the  \\  \  I,  \TI,  \  III,  IX,  X. 
and  XII.  ' 

The  medulla  oblongata  or  bulb  is  the  continuation  upward  of  the 
spinal  cord  and  extends  from  the  lower  limit  of  the  pyramidal  decussa- 
tion below  to  the  lower  margin  of  the  pons  above." 


Fig.  294. — Principal  afferent  and  efferent  suprasegmental  pathways  (excepting  the 
rhinopalHal  connections,  the  eilerent  connections  of  the  midbrain  roof  and  the  olivo- 
cerebellar connections) .  Efferent  peripheral  neurones  of  cranial  nerves  are  omitted.  Each 
neurone  group  (nucleus  and  fasciculus)  is  indicated  by  one  or  several  individual  neurones. 
Decussations  of  tracts  are  indicated  by  an  X.  ac,  Acoustic  radiation,  from  medial  genicu- 
late body  to  temporal  lobe;  br.  conj,  brachium  conjunctivum  (superior  cerebellar  peduncle) : 
brachium  pontis,  from  pons  to  cerebellum  (not  labeled);  h.q.i,  brachium  quadrigeminum 
inferius;  c.g.l,  lateral  or  external  geniculate  body;  c.g.m,  medial  or  internal  geniculate 
body;  c.qiiad,  corpora  quadrigemina;  f.cort.-sp,  cortico-spinal  fasciculus  (pyramidal  tract): 
/.  c.-p.f,  frontal  cortico-pontile  fasciculus  (from  frontal  lobe);  f.c.-p.t,  temporal  cortico- 
pontile  fasciculus  (from  temporal  lobe) ;  f.c.-p.o,  occipital  cortico-pontile  fasciculus  (from 
occipital  \ohe):  f.c It )i,  fasciculus  cuneatus  (column  of  Burdach);  t.f.-b.  fastigio-bulbar 
tract ;/.^rac,  fasciculus  gracilis  (column  of  GoW) ;  f.s.-l,  spino-thalamic  fasciculus;  f.sp.-c.d. 
dorsal  spino-cerebellar  fasciculus  (tract  of  Flechsig);  f.sp.-c.v,  ventral  spino-cerebellar 
fasciculus; /e;«. /a/,  lateral  lemniscus  or  lateral  fillet;  lem.  nied,  medial  lemniscus  or  tillet; 
u.coch,  cochlear  nerve;  ii.cun,  (terminal)  nucleus  of  the  column  of  Burdach;  n.d,  nucleus 
of  Deiters;  n.dent,  nucleus  dentatus;  ;/._?rof,  nucleus  of  the  column  of  Goll;  n.opt,  optic 
nerve;  ;;.r,  nucleus  ruber;  n.l.  nucleus  tecti  (or  iastign);  u.trig,  trigeminal  nerve;  Ji.vest. 
vestibular  nerve;  pes.  ped,  pes  pedunculi  (crusta) ;  pulv.  thai,  pulvinar  thalami;  pyr.  pyramid ; 
rad.  ant,  ventral  spinal  root;  rad.  post,  dorsal  spinal  root;  rad.  opt,  optic  radiation  (from 
lateral  geniculate  body  to  calcarine  region);  sodices,  bundles  from  thalamus  to  postcentral 
region  of  neopallium;  sp.  gang,  spinal  ganglion;  t.f.-b. ^  tractus  fastigio-bulbaris;  thai. 
thalamus;  t.n.d,  tract  from  the  nucleus  of  Deiters;  /.  rub.-sp,  rubro-spinal  tract  (von 
Alonakow).      (Lateral  view  of  brain.) 

'  It  is  better  probably  to  reckon  the  so-called  medullary  part  of  the  XI  with  the  X. 
-It  would  be  better  to  include  in  the  term  medulla  oblongata  what  here  falls  under 
pontile  tegmentum  of  the  hindbrain. 


430 


THE  ORGANS. 


Externally,  the  medulla  shows  the  continuation  upward  of  the 
anterior  fissure  and  posterior  septum  of  the  cord.  On  either  side  of 
the  anterior  fissure  is  a  prominence  caused  by  the  anterior  pyramid, 
and  to  the  outer  side  of  the  pyramid  the  bulging  of  the  olivary  body 
may  be  seen.  The  antero-lateral  surface  of  the  medulla  is  also 
marked  by  the  exit  of  the  fifth  to  the  twelfth  (inclusive)  cranial  nerves. 
The  posterior  surface  shows  two  prominences  on  either  side.  The 
more  median  of  these,  known  as  the  clava,  is  caused  by  the  nucleus 


Corp.  mamillaria     - 
Corp.  pineale 
Colliculus  sup.    -■- 
Colliculus  inf 


Eminentia  med. 
r  Olive  (in  A) 
I.  Area  acustica  (in  B) 

Eminentia  med. 
Ala  cinerea 


Clava 

Dec.  pyramids  1 

Tub.  cuneatum  / 

Tub.  cinereum 


Fig.  297 
Fig.  296 


Fig.  295. — Ventral  (A)  and  dorsal  (B)  views  of  part  of  Brain  Stem  (cerebellum 
removed).  Structures  named  at  the  left  are  indicated  by  their  reference  lines  running  to 
an  X.  On  the  right  are  named  the  figures  showing  transverse  sections  through  the  brain 
at  the  levels  indicated  by  the  reference  lines.  The  level  for  Fig.  31Q  is  not  accurately 
indicated. 


gracilis,  or  nucleus  of  the  column  of  Goll;  the  other,  lying  just  to  the 
outer  side  of  the  clava,  is  due  to  the  nucleus  cuneatus  or  nucleus 
(jf  the  column  of  Burdach.  Lateral  to  this  is  a  third  eminence,  the 
tuberculum  cinereum,  due  in  part  to  the  descending  root  of  the  V, 
merging  anteriorly  with  the  eminence  of  the  restiform  body.  The  cen- 
tral canal  of  the  cord  continues  into  the  medulla,  where  it  gradually 
approaches  the  dorsal  surface  and  opens  into  the  cavity  of  the  fourth 
ventricle.  The  floor  of  the  fourth  ventricle  exhibits  a  medial  eminence 
occupied  caudally  by  the  nucleus  hypoglossi.  Lateral  to  this  is  a  tri- 
angular area,  the  ala  cinerea,  surrounded  by  furrows.  This  is  partly 
occupied  by  nuclei  of  the  vagus.     Forward  and  laterally  a  broader 


THE  NERVOUS  SYSTEM.  431 

triangular  area  with  an  angle  directed  into  the  lateral  recess  marks 
the  area  occupied  by  the  nuclei  of  the  acoustic  nerve.  Still  further 
forward  near  the  median  line  are  eminences  indicating  the  positions  of 
the  nucleus  abducentis  and  genu  facialis.  The  roof  of  the  fourth  ven- 
tricle is  formed  by  the  thin  plexus  chorioideus  and  the  cerebellum. 
(Fig.  295.) 

The  pons  is  a  mass  of  fibres  and  gray  matter  extending  across  the 
ventral  surface  of  portions  of  mid-  and  hindbrain.  The  term  is  often 
used  to  include  the  whole  of  the  basal  part  of  the  brain  thus  covered 
by  the  pons.  It  is  better,  however,  to  restrict  it  to  the  pons  itself. 
The  part  of  the  hindbrain  dorsal  to  the  pons,  which  is  the  continuation 
forward  of  the  medulla,  may  be  included  in  the  term  tegmentum  of  the 
hindbrain. 

The  cerebellum  is  described  on  p.  455. 

TECHNIC. 

The  technic  of  the  medulla  (and  the  rest  of  the  segmental  brain)  is  the  same 
as  that  of  the  cord  (page  421).  Transverse  sections  should  be  cut  through  the 
following  typical  levels,  stained  by  Weigert's  method  (page  29),  and  mounted  in 
balsam: 

1.  Through  the  pyramidal  decussation. 

2.  Through  the  sens-ory  decussation. 

3.  Through  the  lower  part  of  the  olivary  nucleus. 

4.  Through  the  middle  of  the  olivary  nucleus. 

5.  Through  the  entrance  of  the  cochlear  nerve. 

6.  Through  the  entrance  of  the  vestibular  nerve. 

7.  Through  the  roots  of  the  sixth  and  seventh  cranial  nerves. 

8.  Through  the  root  of  the  fifth  cranial  nerve. 

The  methods  of  Nissl,  Cajal  and  glia  stains  should  also  be  used  when 
practicable. 

PRACTICAL  STUDY. 

I.  Transverse  Section  of  the  Medulla  through  the  Decussation  of  the  Pyram- 
idal Tracts  (Motor  Decussation)   (Figs.  295  and  296). 

The  most  conspicuous  features  of  this  section  are  the  decussation  of  the  pvra- 
mids,  the  larger  size  of  the  dorsal  horn  and  the  beginning  of  the  gray  reticular 
formation.     Surrounding  the  central  canal  is  the  central  gray. 

Efferent  Peripheral  Neurones,— Nuclei  of  first  cervical  spinal  nerve  in  ventral 
gray,  and  root  fibres  passing  out  to  emerge  on  ventral  aspect.  Xuclei  of  XI,  in 
mesial  position  in  central  gray,  or  in  ventral  gray.  A.xones  pass  out  laterally 
from  latter  and  emerge  on  the  lateral  surface.  The  mesial  or  deep  nuclei  are 
best  reck(Micd  with  nerve  X. 


432 


THE  ORGANS. 


THE  XER\'OUS  SYSTEM.  433 

Afferent  Roots,  their  Terminal  Nuclei  and  Secondary  Tracts. — Some 
afferent  fibres  of  the  first  cervical  spinal  nerve  are  still  entering  at  this  level. 

Ascending  afferent  roots:  The  dorsal  funiculus  comprising  the  fasciculus 
cuneatus  and  fasciculus  gracilis  remain  as  in  the  cord.  Collaterals  and  terminals 
from  them  can  be  seen  entering  the  subjacent  gray. 

Descending  afferent  roots:  Some  of  the  fine  fibres  between  the  enlarged  dorsal 
horn  and  the  periphery,  occupying  the  position  of  the  zone  of  Lissauer  in  the  cord, 
are  descending  afferent  root  fibers  of  the  V-cranial  nerve  or  tractus  spinalis  trigemini 
{spinal  V).  Collaterals  and  terminals  from  these  fibres  terminate  in  the  gelatinous 
substance  of  Rolando  and  also  traverse  it  to  form  a  plexus  of  meduUated  fibres  in 
its  inner  side  very  similar  to  the  cord.  The  axones  of  the  dorsal  horn  cells  (or 
terminal  nucleus  of  the  V)  form  the  secondary  tracts  of  the  V,  which  cannot  be 
distinguished  (p.  452  and  Fig.  307). 

Secondary  tracts,  forming  parts  of  afferent  suprasegmental  paths:  These  form 
a  mass  of  fibres  along  the  lateral  periphery  of  the  medulla  which  consists  of  (a)  the 
dorsal  spino-cerebellar,  (b)  the  ventral  spino-cerebellar  and  (c)  the  spino-thalamic 
tracts. 

Intersegmental  Neurones. — The  neurone  bodies  are,  as  in  the  cord,  scattered 
throughout  the  gray.  The  continuation  of  the  ventro-lateral  intersegmental  tracts 
of  the  cord  (and  the  tecto-spinal  tract)  is  the  U-shaped  mass  of  fibres  around  the 
ventral  gray.  This  mass  consists  of  the  long  descending,  the  shorter  ascending  and 
descending  intersegmental  tracts,  and  the  tecto-spinal;  i.e.,  (a)  rubro-spinal  (in 
lateral  arm  of  U),  (b)  vestibulo-spinal  (lateral  and  mesial),  (c)  tract  from  interstitial 
nucleus  of  Cajal  (mesial),  (d)  tecto-spinal  (mesial),  (e)  shorter  descending  and 
ascending  tracts  which  may  be  regarded  as  the  equivalent  of  the  ground  bundles 
of  the  cord  comprising  shorter  reticulo-spinal  and  spino-reticular  fibres.  The 
shortest  of  these  fibres,  which  in  the  cord  were  next  the  lateral  gray,  are  now  mingled 
with  the  gray,  the  combination  constituting  the  gray  reticular  formation.  Other 
short  intersegmental  tracts  lie  in  and  adjoining  the  dorsal  horn,  as  in  the  cord. 

Descending  suprasegmental  paths  include  certain  of  the  long  descending  inter- 
segmental tracts  as  previously  explained.  Besides  these  there  are  efferent  supraseg- 
mental neurones  known  as  the  pallio-spinal  or  pyramidal  tracts  and  the  tecto-spinal 
tracts.  Bundles  of  fibres  are  seen  crossing  {pyramidal  decussation)  from  the  an- 
terior pyramid  of  one  side  to  the  opposite  dorso-lateral  column,  where  they  turn 
downward  as  the  crossed  pyramidal  tract.  In  their  passage  through  the  gray 
matter,  they  cut  off  the  ventral  horn  from  the  rest  of  the  gray  matter.  These  fibres, 
as  already  noted  in  the  cord,  are  descending  axones  from  motor  cells  situated  in  the 
precentral  cerebral  cortex.  In  the  pyramidal  decussation  most  of  these  fibres  cross 
to  the  opposite  dorso-lateral  region  to  pass  down  the  cord  as  the  crossed  pyramidal 
tract  (p.  416,  and  Fig.  289;  Fig.  293,  F).  A  few  remain  in  their  original  anterior 
position  to  continue  down  the  cord  as  the  direct  pyramidal  tract  (p.  417,  and  Fig. 
289;  Fig.  293,  F).  A  few  pass  to  the  ventral  tract  in  the  same  side,  thus  being 
uncrossed  fibres  in  the  lateral  tract.  The  bundles  of  fibres  do  not  cross  in  a  trans- 
verse plane,  but  take  a  downward  direction  at  the  same  time.  For  this  reason  trans- 
verse sections  show  these  fibres  cut  rather  obliquely.  Because  of  the  fact  that  the 
fibres  cross  in  alternate  bundles,  the  number  of  decussating  fibres  seen  in  any  one 
section  is  greater  on  one  side  than  on  the  other  (Fig.  295). 
28 


434 


THE  ORGANS. 


THE  NERVOUS  SYSTEM.  435 

2.  Transverse  Section  of  the  Medulla  through  the  Decussation  of  the  Fillet 
or  Lemniscus  (Sensory  Decussation;  (Figs.  295  and  297). 

The  most  conspicuous  features  are  the  appearance  of  the  nuclei  cuneatus  and 
gracilis,  the  decussation  and  formation  of  the  medial  lemniscus  or  iillet,  and  the 
increase  of  the  gray  reticular  formation. 

Peripheral  Efferent  Neurones. — In  the  lateral  part  of  the  central  gray  is  the 
dorsal  nucleus  of  the  X  {nucleus  alee  cinerece).  In  the  ventral  part  of  the  central 
gray  is  the  nucleus  hypoglossi  and,  passing  ventrally  and  emerging  lateral  to  the 
pyramids,  may  be  seen  the  axones  of  its  cells — the  root  fibres  of  the  XII. 

In  the  nucleus  XII  can  be  distinguished  (Weigert  stain)  coarse  fibres  which 
are  the  root  fibres,  and  fine  fibres  which  are  terminals  of  other  fibres  ending  in  the 
nucleus.  Among  these  have  been  distinguished  collaterals  from  secondary  vago- 
glossopharyngeal and  trigeminal  tracts  (three-neurone  reflex).  Whether  pyram- 
idal fibres  reach  the  nucleus  directly  or  z'ia  intercalated  neurones  is  uncertain. 

Afferent  Roots,  their  Terminal  Nuclei  and  Secondary  Tracts. — Entering 
afferent  root  fibres  are  usually  not  present. 

The  funiculi  or  fasciculi  cuneatus  and  gracilis  have  diminished,  and  internal 
to  them  have  appeared  large  masses  of  gray.  These  are  the  nuclei  of  the  columns, 
and  are  known,  respectively,  as  the  nucleus  of  the  column  of  Goll  or  the  nucleus 
gracilis,  and  the  nucleus  of  the  column  of  Burdach  or  the  nucleus  cuneatus.  In  the 
higher  sensory  decussation  levels  there  is  usually  an  accessory  cuneate  nucleus. 

These  nuclei  serve  as  nuclei  of  termination  for  the  fibres  of  the  posterior  funiculi. 
Their  termination  in  these  nuclei  is  the  ending  of  that  system  of  fibres  which  has 
been  traced  upward  from  their  origin  in  the  cells  of  the  spinal  ganglia;  the  comple- 
tion of  the  course  of  the  spinal  peripheral  afferent  neurones.  As  the  fibres  of  the 
posterior  columns  are  constantly  terminating  in  these  nuclei,  there  is,  in  passing 
from  below  upward,  a  constant  increase  in  the  size  of  the  nuclei  and  a  correspond- 
ing decrease  in  the  size  of  the  posterior  columns,  until,  just  below  the  olive,  the  whole 
of  the  column  of  Goll  and  most  of  the  column  of  Burdach  are  replaced  by  their 
respective  nuclei.      (Pp.  413,  414.) 

Study  the  plexus  of  fine  fibres  in  these  nuclei,  formed  by  the  terminals  of  the 
column  fibres,  also  the  coarser  fibres  (axones  of  the  cells  of  the  nuclei)  gathered  in 
the  ventral  part  of  the  nuclei,  whence  they  emerge  and  curve'  around  the  central 
gray,  cross  to  the  opposite  side  ventral  to  it  and  dorsal  to  the  pyramids,  and  then 
turn  brainward  forming  the  bundle  of  fibres  known  as  the  medial  lemniscus  or  fillet. 

The  spinal  V  has  increased  and  also  its  terminal  nucleus,  the  dorsal  horn.  The 
spino-cerebellar  and  spino-thalamic  tracts  occupy  about  the  same  positions. 

In  the  central  gray  dorsal  to  the  central  canal  is  a  nucleus  representing  a 
union  of  the  caudal  ends  of  the  terminal  nuclei  of  the  fasciculi  solitarii  (see  next 
section) — the  nucleus  commissuralis.  Fibres  of  the  fasciculi  solitarii  also  de- 
cussate here. 

Intersegmental  Neurones. — The  rubro-spinal  tract,  tracts  from  Deiters' 
nucleus  and  interstitial  nucleus  of  Cajal  occupy  about  the  same  positions.     The 

'Fibres  having  a  transverse  curved  or  arched  course  are  in  general  termed 
arcuate  fibres.  If  they  are  deeply  located,  they  are  inlernal  arcuate  fibres,  if  near  the  per- 
iphery, they  are  superficial  or  external  arcuate  fibres.  Obviously  the  same  fibre  may  be,  in 
different  parts  of  its  course,  internal  arcuate,  e.xternal  arcuate,  and  longitudinal. 


436 


THE  ORGANS. 


oi 

> 

o 

o 

u 

O 

a; 

x; 

THE  NERVOUS  SYSTEM. 


437 


reticular  formation  has  increased,  the  whole  of  the  ventral  horn  and  intermediate 
gray  containing  bundles  of  longitudinal  fibres.  The  formation  is  also  traversed  by 
transverse  fibres,  representing  the  beginnings  or  terminations  of  various  longi- 
tudinal fibres. 

Efferent  Suprasegmental  Neurones. — The  decussation  of  the  pyramids  has 
now  nearly  or  entirely  ceased.  The  lateral  pyramidal  tracts  are  no  longer  in  the 
lateral  columns  but  are  part  of  the  anterior  pyramidal  tract  which  forms  two 
large  masses  of  fibres  on  each  side  of  the  ventral  sulcus.  The  tecto-spinal  tract 
occupies  the  same  position. 


3.  Transverse  Section  of  the  Medulla  through  the  Lower  Part  of  the  Inferior 
Olivary  Nucleus  (Figs.  295  and  298). 

The  central  canal  has  opened  into  the  fourth  ventricle,  the  central  gray  (includ- 
ing the  central  gelatinous  substance)  now  being  spread  out  on  its  floor.  The  roof 
of  the  ventricle  is  formed  by  its 
chorioid  plexus.  The  most  con- 
spicuous new  feature  is  the  olive. 

Efferent  Peripheral  Neurones. 
— The  nucleus  of  the  XII  is  large 
and  occupies  a  swelling  in  the  floor 
of  the  ventricle  each  side  of  the 
median  line,  known  as  the  "emi- 
nentia"  hypoglossi.  The  root 
fibres  of  the  XII  pass  lateral  to 
the  medial  lemniscus,  between  the 
olive  and  pyramid,  and  then 
emerge  at  the  groove  between  olive 
and  pyramid. 

The  dorsal  nucleus  of  the  X 
occupies  a  swelling  lateral  to  the 
preceding  and  known  as  the  ala 
cinerea.  Some  of  the  root  fibres 
of  the  X  are  axones  from  this 
nucleus.  They  probably  innervate 
(via  the  sympathetic)  some,  at 
least,  of  the  smooth  muscles,  heart 
and  glands,  innervated  by  the 
vagus  (X). 

The  bodies  of  another  group  of 
peripheral  eft'erent  neurones  form 
the  nucleus  amhiguus,  often   diffi- 


FiG.  299. — Diagram  of  Origin  of  Cranial  Nerves 
XandXII.  (Schafer.)  /)_vr,  Pyramid;  o,  olivary 
nucleus;  r,  restiform  body;  d.V,  spinal  root  of 
fifth  nerve;  n.XII,  nucleus  of  hypoglossal;  XII, 
hypoglossal  nerve;  d.n.X.XI,  dorsal  nucleus  of 
vagus;  n.amh,  nucleus  ambiguus;  f.s.,  solitary 
fasciculus  (descending  root  of  vagus  and  glosso- 
pharyngeal) ;  f.s.n,  nucleus  of  solitary  fasciculus ; 
A',  motor  fibre  of  vagus  from  nucleus  ambiguus; 
g,  ganglion  cell  of  sensory  root  of  vagus  sending 
central  arm  into  solitary  fasciculus  {f.s.)  and 
collateral  to  its  nucleus  {f.s.n.);  f.s.n,  cell  of 
nucleus  of  solitary  fasciculus  sending  axone  as 
internal  arcuate  fibre  to  opposite  side  of  cord 
(secondary  vagus  and  glosso-pharyngeal  tract.) 
This  course  of  the  secondarv  tract  is  doubtful. 


cult  to  distinguish,  in  the  reticular 

formation.  Their  axones  pass  obliquely,  dorsally  and  mesially,  join  the  other 
root  fibres  of  the  X,  and  then  bending  abruptly,  pass  with  them  to  the  lateral 
surface  of  the  medulla.  Some  of  them  probably  innervate  the  striated  muscles 
of  the  larynx.      (Fig.  290). 


438  THE  ORGANS. 

Afferent  Peripheral  Roots,  their  Terminal  Nuclei  and  Secondary  Tracts. — 

Other  root  fibres  are  the  afferent  fibres  of  the  X  which  form  a  common  root  with  the 
preceding.  Sometimes  they  can  be  seen  joining  the  fasciculus  soHtarius  of  which 
they  form  a  part.  Some  fibres  or  collaterals  may  enter  the  adjacent  gray  {terminal 
nucleus  of  the  X)  (see  page  437,  Fig.  299). 

If  the  roots  of  the  X  do  not  show  well  in  the  section,  defer  their  study  until  the 
following  section  where  the  IX  shows  similar  relations. 

The  spinal  V  is  partly  pierced  and  partly  covered  by  transverse  fibres,  princi- 
pally olivo-cerebellar  fibres  (see  below).  Its  terminal  nucleus  is  less  conspicuous. 
Two  new  bundles  of  descending  root  fibers  have  appeared;  one  is  the  fasciculus 
solitarius  composed  of  the  afferent  root  fibres  of  the  X,  IX  (including  gustatory 
fibres),  and,  higher  up,  of  the  VII.  A  small  mass  of  gray  of  a  gelatinous  appear- 
ance near  it  is  its  terminal  nucleus.  The  course  of  the  secondary  tract  cannot  be 
made  out  and  is  not  accurately  known.  The  other  bundle  is  the  descending  vestib- 
ular root.  It  lies  lateral  to  the  fasciculus  solitarius.  Accompanying  it  are  cells 
which  constitute  its  terminal  nucleus.  Occupying  the  floor  of  the  ventricle  lateral 
to  the  dorsal  nucleus  of  the  X  is  another  terminal  nucleus  of  the  vestibular  nerve, 
the  nucleus  medialis  (triangular  or  chief  nucleus).  Internal  arcuate  fibres  emerg- 
ing from  these  regions  may  represent  secondary  tracts  (probably  reflex)  from  these 
nuclei.     (P.  441;  Fig.  302.) 

The  nucleus  gracihs  has  disappeared.  The  nucleus  cuneatus  may  be  present, 
much  diminished,  and  give  rise  to  some  internal  arcuate  fibres  to  the  medial  lemnis- 
cus. The  lemniscus  is  now  a  tract  which  has  become  built  up  on  each  side  of  the 
median  line.  This  latter  is  known  as  the  raphe  (i.e.,  "seam,"  stitched  by  the  decus- 
sating fibres). 

The  ventral  spino-cerebellar  tract  and  spino-thalamic  tract  are  in  about  the 
same  lateral  position,  but  the  dorsal  spino-cerebellar  tract  has  moved  dorsally  and 
together  with  olivo-cerebellar  fibres  (see  below)  begins  to  form  the  restiform  body 
(see  below). 

In  the  lateral  part  of  the  reticular  formation,  between  spinal  V  and  olive  are 
seen  the  nuclei  laterales.  In  these  nuclei  some  of  the  spino-cerebellar  fibres  end. 
The  axones  of  these  nuclei  partly  enter  the  restiform  body  on  the  same  side  and 
partly  cross  to  the  opposite  restiform  body  (p.  455;  Fig.  308).  They  form  some  of  the 
ventral  external  arcuate  fibres  seen  in  the  section.  The  lateral  nuclei  are  thus  partial 
interruptions  in  the  spino-cerebellar  path.     The  nuclei  arcuati  are  well  marked. 

Other  Afferent  Cerebellar  Neurones. — A  new  and  important  convoluted  mass 
of  gray  is  the  inferior  olivary  nucleus,  forming  a  bulging  in  the  lateral  surface  of  the 
medulla  known  as  the  olive.  Near  it  are  the  dorsal  and  medial  accessory  olives.  The 
axones  of  the  olivary  cells  are  the  olivo-cerebellar  fibres.  They  cross  through  the 
fillets,  pass  through  or  around  the  opposite  olivary  nucleus,  thence  proceed  dorso- 
laterally,  being  gathered  into  more  compact  bundles,  traverse  or  surround  the  spinal 
V  and  dorsal  to  it  bend  longitudinally,  forming  a  great  part  of  the  restiform  body. 
The  latter  produces  an  eminence  on  the  dorso-lateral  surface  of  the  medulla.  The 
restiform  Ijody,  thus  formed  by  these  spino-cerebellar  and  olivo-cerebellar  fibres, 
together  with  certain  others,  passes  into  the  cerebellum  higher  up,  forming  the  major 
part  of  the  inferior  cerebellar  arm  or  peduncle.     (Comp.  p.  455.) 

I'ibres  appearing  on  the  external  surface  of  the  olivary  nucleus  are  the  termina- 


THE  NERVOUS  SYSTEM.  439 

tion  of  a  large  tract  descending  to  the  olivary  nucleus,  the  central  tegmental  tract. 
Its  origin  in  higher  levels  is  not  accurately  known,  but  is  possibly  the  nucleus  lentic- 
ularis  of  the  endbrain. 

Intersegmental  Neurones. — The  reticular  formation  is  now  still  more 
extensive. 

The  original  U-shaped  mass  of  intersegmental  tracts  (and  the  tecto-spinal  tract) 
has  now  become  widely  separated  into  two  parts.  The  lateral  part  consisting 
principally  of  the  rubro-spinal  tract  and  uncrossed  fibres  from  Deiters'  nucleus  lies 
mesial  to,  or  partly  mingled  with,  the  spino-thalamic  and  ventral  spino-cerebellar 
tracts.  The  mesial  part  of  the  U,  consisting  principally  of  crossed  and  uncrossed 
fibres  from  Deiters'  nucleus  and  other  nuclei  in  the  reticular  formation,  and  of  fibres 
from  the  interstitial  nucleus  of  Cajal,  now  forms  the  medial  longitudinal  fasciculus 
dorsal  to  the  fillet.  Near  this  bundle  or  united  with  it,  is  the  tecto-spinal  tract 
(predorsal  tract).  When  these  tracts  have  passed  down  to  below  the  formation  of 
the  fillet  and  the  olives,  they  assume  the  positions  noted  in  the  lower  levels  of  the 
medulla. 

Efferent  Suprasegmental  Neurones. — The  pyramids  are  the  same.  Small 
bundles  of  more  lightlv  stained  fibres  present  in  the  fillet  here  and  in  higher 
levels  (Weigert  stain,  not  indicated  in  the  figures)  are  efferent  pallia!  fibres  detached 
from  pes  or  pyramids.  They  are  aberrant  fibres  which  rejoin  the  pyramids  or  are 
fibres  innervating  motor  cranial  nuclei.     The  tecto-spinal  tract  (see  above). 

4.  Transverse  Section  of  the  Medulla  through  the  Middle  of  the  Olivary 

Nucleus. 

Such  a  section  is  so  similar  to  3  and  5  that  its  detailed  description  may  be  omitted. 
The  nucleus  cuneatus  has  disappeared;  the  fillet  increased  somewhat;  fasciculus 
solitarius  and  descending  vestibular  root  have  increased;  also  their  terminal  nuclei. 
The  olivary  nucleus,  olivo-cerebellar  fibres,  and  the  restiform  body  have  greatly 
increased.     The  formatio  reticularis  has  increased  in  extent. 

5.  Transverse  Section  of  the  Medulla  through  the  Entrance  of  the  Cochlear 

Root  of  Nerve  VIII.      (Figs.  295  and  300.) 

Efferent  Peripheral  Neurones. — The  dorsal  vagus  nucleus  is  not  present,  but 
the  nucleus  ambiguus  is  usually  present  and  probably  sends  some  axones  to  nerve 
IX,  passing  out  with  the  aft'erent  fibres  (see  below).  The  nucleus  XII  has  disap- 
peared and  also  its  root  fibres. 

Afferent  Roots,  their  Terminal  Nuclei  and  Secondary  Tracts. — Usually 
the  afferent  root  fibres  of  nerve  IX  are  present.  They  enter  on  the  lateral  aspect 
of  the  medulla  ventral  to  the  restiform  body,  traverse  the  spinal  V,  and  pass  to  the 
fasciculus  soHtarius  or  its  terminal  nucleus.  The  fasciculus  solitarius  is  smaller, 
and  just  above  the  entrance  of  the  IX  consists  of  only  a  comparatively  few  descend- 
ing afferent  root  fibres  of  the  VII. 

The  fibres  of  the  cochlear  nerve  enter  the  extreme  lateral  angle  of  the  medulla, 
where  many,  or,  according  to  some,  all  of  them  terminate  in  two  masses  of  cells 
enveloping  externally  the  restiform  body  and  known  as  the  ventral  (or  accessory)  and 


440 


THE  ORGANS. 


/C,  o-r; 


2S  ^° 


THE  NERVOUS  SYSTEIM.  441 

dorsal  (or  lateral)  cochlear  nuclei.  Most  of  the  axones  of  the  dorsal  nucleus  pass 
across  in  the  floor  of  the  ventricle  {strice  medullar es)  to  form  a  part  of  the  opposite 
secondary  tract  {lateral  lemniscus)  of  the  cochlear  nerve.  The  axones  of  the  ventral 
nucleus  also  decussate,  but  by  a  more  ventral  route,  and  also  form  a  part  of  the  lat- 
eral lemniscus.  This  latter  decussation  takes  place  at  a  higher  level  (see  next 
section). 

The  auditory  nerve  is  divided  into  two  parts:  the  cochlear  nerve  (ganglion 
spirale)  and  the  vestibular  nerve  (ganglion  of  Scarpa) .  The  fibres  of  the  cochlear  root 
enter  at  a  lower  level  than  those  of  the  vestibular.  Some  of  them  enter  the  ventral 
cochlear  nucleus;  the  remainder  pass  dorsalward  to  the  dorsal  cochlear  nucleus,  or 
nucleus  of  the  acoustic  tubercle.  According  to  some  authorities,  some  root  fibres 
pass  to  the  superior  olivary  and  trapezoid  nuclei.  The  axones  of  the  cells  of  the 
ventral  and  dorsal  nuclei  form  the  secondary  cochlear  tract  (lateral  fillet).  These 
fibres  decussate  (trapezius)  and  send  collaterals  to,  or  are  partially  interrupted  in, 
the  nucleus  olivaris  superior,  trapezoideus,  nucleus  of  lateral  fillet  and  posterior 
corpus  quadrigeminum.  According  to  some  authorities  all  the  fibres  of  the  lateral 
lemniscus  terminate  in  the  posterior  corpus  quadrigeminum.  From  the  posterior 
corpus  quadrigeminum,  the  path  is  formed  by  the  arm  or  brachium  of  the  latter  to 
the  medial  geniculate  body  and  thence  to  the  temporal  cortex  cerebri.  It  is  thus 
not  possible  to  state  definitely  how  many  neurone  systems  are  involved,  but  the 
principal  ones  are:  (i)  ganglion  spirale,  (2)  dorsal  and  ventral  nuclei  and  (decussa- 
tion) lateral  lemniscus,  (3)  posterior  corpus  quadrigeminum  and  its  brachium,  (4) 
medial  geniculate  body  of  the  thalamus  and  geniculo-cortical  fibres.  If  the  lateral 
lemniscus  fibres  be  regarded  as  simply  passing  by  the  posterior  corpus  quadrigemi- 
num, giving  collaterals  to  it  (Cajal),  the  path  might  in  part  consist  of  three  neurone 
systems  analogous  to  those  of  the  paths  from  the  cord,  trigeminus  and  eye.  (Figs. 
294,  301.) 

The  fibres  of  the  vestibular  root  enter  higher  and  mesial  to  those  of  the  cochlear 
root,  passing  dorsally  along  the  inner  side  of  the  restiform  body  to  four  terminal 
nuclei,  which  cannot  all  be  clearly  seen  in  any  one  section;  (a)  Deiters'  nucleus 
(lateral  vestibular  nucleus)  situated  at  the  end  of  the  main  bundle  of  root  fibres, 
just  internal  to  the  restiform  body;  {b)  von  Bechterew's  nucleus  (superior  vestibular 
nucleus)  situated  somewhat  dorsal  to  Deiters'  nucleus  in  the  lateral  wall  of  the 
fourth  ventricle;  (c)  the  median  or  principal  nucleus  of  the  vestibular  division — a 
large  triangular  nucleus,  occupying  a  considerable  part  of  the  floor  of  the  fourth 
ventricle;  {d)  the  descending  vestibular  nucleus  which  accompanies  the  descend- 
ing fibres  of  the  vestibular  root  (spinal  eighth).  Fibres  also  pass  to  the  cerebellum. 
The  axones  of  the  cells  of  the  terminal  vestibular  nuclei  form  the  secondary  vestib- 
ular tracts,  some  axones  going  to  (a)  the  cerebellum  (?),  (b)  the  midbrain,  espe- 
cially to  the  nuclei  of  nerves  III  and  IV  {via  Deiters  and  von  Bechterew,  the  former 
by  the  medial  longitudinal  fasciculus),  (c)  the  medulla  and  cord,  probably  to  vari- 
ous motor  nuclei,  via  the  medial  longitudinal  fasciculus,  lateral  tract  from  Deiters' 
nucleus  and  other  tracts  in  the  reticular  formation.  (Figs.  294,  302  and  308.) 

The  descending  vestibular  root  is  large,  as  is  also  its  terminal  nucleus  and  the 
medial  terminal  vestibular  nucleus,  in  the  present  section. 

The  spinal  V  is  unchanged,  its  terminal  nucleus  being  rather  indistinct.  Second- 
ary trigeminal  tracts  cannot  be  distinguished — such  fibres  probably  either  join  the 


442 


THE  ORGANS. 


L«mniscu5 


Lemniscus.  .       /,-  ; 
Nu.  Urrj.  l<Lt./jJ..  !,' 


.Lemniscus  latiVLJh 


'^°"n-  '■et.c.  te<frqen^^  \\C 


Nu.  Corfi  -trape^oidei 
- Oliva.  superior 


il)ira.lii\  __^ ,    , 

Nu  accessortus  '  ' 


I'iG.   30[ 


THE  NERVOUS  SYSTEM.  443 


EXPLANATION  OF  FIG.  301 

Fig.  301. — Diagram  showing  Connections  of  the  Cochlear  Portion  of  the  Auditor}' 
(VIII)  Nerve.  A,  Section  at  level  of  anterior  corpora  quadrigemina  and  red  nucleus;  B, 
through  level  of  posterior  corpora  quadrigemina;  C,  through  level  of  nucleus  of  lateral 
lemniscus  (Nu.  lem.  lat.);  D,  through  pons  at  level  of  VIII  nerve.  Spacing  between  the 
different  levels  is  not  proportionate.  In  B  and  C  the  basis  pedunculi  is  omitted.  Each 
neurone  group  is  indicated  by  one  or  several  individual  neurones. 

Neurone  No.  i. — Cell  bodies  in  spiral  ganglion  (gang,  spiralis);  peripheral  processes 
end  in  organ  of  Corti;  central  processes  terminate  principally  in  ventral  or  accessory 
nucleus  (Nu.  accessorius)  and  lateral  nucleus  (Nu.  lateralis)  or  tuberculum  acusticum; 
some  also  terminate  in  superior  olives  (Oliva  superior),  and  nuclei  of  trapezoid  body  (Nu. 
corp.  trapezoidei)  of  same  and  opposite  sides. 

Neurone  No.  2.  (or  3  ?). — Axones  of  cells  in  accessory  nucleus,  in  superior  olives,  and  in 
nuclei  of  trapezoid  body,  constitute  a  ventral  path  in  the  lower  border  of  the  tegmentum, 
and  form  the  lateral  part  of  the  lateral  lemniscus  (Lemniscus  lateralis)  or  lateral  fillet  on 
the  opposite  side.  A.xones  of  cells  in  the  lateral  nucleus  traverse  the  floor  of  the  fourth  ven- 
tricle as  the  striae  medullares,  forming  a  dorsal  pathway,  decussate  and  then  turn  ventrally 
to  a  point  dorsal  to  the  superior  olive  and  join  the  lateral  lemniscus  as  its  mesial  part . 
Some  axones  also  of  cells  in  the  accessory  and  lateral  nuclei  pass  dorsally,  looping  around  the 
restiform  body,  and  then  proceed  ventrally  (bundle  of  Held)  to  join  the  opposite  lemniscus. 
The  lateral  lemniscus  passes  upward  to  the  posterior  corpus  quadrigeminum,  some  of  the 
a.xones  terminating  en  route  in  the  nucleus  of  the  lateral  lemniscus.  From  cells  in  this 
nucleus  some  axones  again  join  the  lateral  lemniscus,  and  a  few  decussate  and  then  pass 
upward  to  the  posterior  corp.  quad.  The  axones  of  the  lateral  lemniscus  terminate  in  the 
posterior  corp.  quad.,  or  pass  on  to  terminate  in  the  internal  geniculate  body,  merely  giving 
off  collaterals  to  the  post.  corp.  quad.  Some  fibres  of  the  lateral  lemniscus  probably  go  to 
the  ant.  corp.  quad. 

Neurone  No.  3  (or  4?). — .'Axones  of  cells  in  the  gray  matter  of  the  posterior  corp.  quad. 
form  its  brachium  (Brachium  corp.  quad,  post.)  and  ascend  to  terminate  in  the  internal 
or  medial  geniculate  body  (Corp.  genie,  inter.). 

Neurone  No.  4  (or  5  ?). — Axones  of  cells  in  the  internal  geniculate  body  pass  as  a  part 
of  the  thalamic  radiation  via  the  posterior  part  of  the  internal  capsule  to  the  cortex  of  the 
temporal  lobe  of  the  cerebrum. 

The  axones  which  constitute  the  ventral  path  (Neurones  i  and  2)  form  a  bundle  of 
tibres  known  as  the  trapezoid  body  (Corpus  trapezoideum).  The  decussation  of  these  is 
peculiar  in  that  the  dorsal  axones  of  the  bundle  on  one  side  become  the  ventral  ones  on  the 
opposite  side;  this  accounts  for  the  convergence  of  the  axones  at  the  median  raphe. 

A.xones  of  cells  in  the  superior  olive  pass  to  the  nucleus  of  VI  nerve  (reflex).  There  is 
possibly  also  a  descending  path  from  the  lateral  nucleus  to  the  spinal  cord  (not  indicated). 


444 


THE  ORGANS. 


/Vu.  n-  vest  dejc 


Garo.  Scdrhae 


redun.  Ltifer. 
cerebedi 


FlO.  ;:;02 


THE  NERVOUS  SYSTEM.  445 


EXPLANATION  OF  FIG.  302. 

Fig.  302. — Principal  Connections  of  the  Vestibular  Portion  of  the  Auditory  (A'^III) 
Nerve.  A,  Section  at  level  of  oculomotor  (III)  nerve;  B,  section  through  pons  and  cerebel- 
lum; C,  through  inferior  olives;  D,  through  spinal  cord.  Each  neurone  group  is  indicated 
by  one  or  several  individual  neurones. 

Neurone  No.  i. — Cell  bodies  in  ganglion  of  Scarpa;  peripheral  processes  end  in  semi- 
circular canals;  central  processes  bifurcate,  and  ascending  arms  go  to  Deiters'  nucleus 
(Nu.  lat.  n.  vestib.)  (i  a),  to  von  Bechterew's  nucleus  (Nu.  sup.  n.  vestib.)  (i  h),  and  to 
nuclei  fastigii  and  cortex  of  vermis  of  cerebellum  (i  c);  descending  arms  go  to  nucleus  of 
descending  root  (Nu.  n.  vestib.  desc.)  {id)  and  (collaterals?)  to  principal  or  median  nucleus 
(Nu.  med.  n.  vestib.)  (i  e). 

Neurone  No.  2. — Axones  of  some  cells  in  Deiters'  nucleus  descend  (2  a,  Tr.  desc.  nu. 
Deitersi)  uncrossed  to  antero-lateral  column  of  the  cord,  axones  of  other  cells  enter  the 
posterior  longitudinal  fasciculus  (Fasc.  long,  post.,  2  b)  of  same  side  and  descend  to  anterior 
column  of  the  cord,  others  pass  to  the  posterior  longitudinal  fasciculus  of  opposite  side 
whence  some  (2  c)  descend  to  anterior  column  of  the  cord,  occupying  a  position  near 
the  anterior  median  fissure,  while  some  (2  d)  ascend  in  the  posterior  longitudinal  fasciculus 
and  terminate  principally  in  the  nuclei  of  VI,  IV,  and  III  nerves.  Axones  of  cells  in  von 
Bechterew's  nucleus  ascend  (2  e),  joining  lateral  part  of  posterior  longitudinal  fasciculus  of 
same  side,  and  terminate  in  nuclei  of  W  and  III  nerves.  Axones  of  cells  in  the  nucleus 
of  the  descending  root  probably  pass  in  part  to  lateral  part  of  reticular  formation  of  same 
and  opposite  sides,  ascending  and  descending  (to  other  motor  nuclei?).  Axones  of  cells 
in  the  median  nucleus  probably  pass  largely  into  the  reticular  formation,  possibly  also  to 
the  posterior  longitudinal  fasciculus  (not  indicated).  Axones  of  cells  in  the  nuclei  fa'stigii 
of  the  cerebellum  pass  to  von  Bechterew's  nucleus  (2/)  and  to  Deiters''nucleus'(2  o^).  The 
cerebellar  associations  intercalated  between  these  (2/,  2^)  and  the  vestibular  fibres  to  the 
cerebellum  (i  c)  are  not  known.  [It  is  evident  that  impulses  other  than  vestibular  ones 
entering  the  cerebellum  may  also  by  2/  and  2  g  act  indirectly  upon  the  motor  nuclei  in- 
nervated by  axones  of  the  cells  in  Deiters'  and  von  Bechterew's  nuclei.  Compare  Figs.  294 
and  308.] 


446 


THE  ORGANS. 


Nvvn 


Fig.  303. — Section  through  the  Hindbrain  at  the  Level  of  the  Junction  of  Pons  and 
Cerebellum  and  the  Entrance  of  the  Vestibular  Part  of  the  Eighth  Nerve.  Weigert 
fireparation.  (Marburg.)  Va,  Radix  spinalis  trigemini  (spinal  root  of  the  fifth);  VI, 
nervus  abducens  (external  eye  muscle  nerve) ;  Vila,  pars  nuclearis  nervi  facialis  (pars 
prima,  crus  of  origin  or  ascending  facial  root);  VIII,  nervus  acusticus  (eighth,  vestibular 
part);  BPo,  brachium  pontis  (middle  cerebellar  peduncle);  ZJrcy,  brachium  conjunctivum 
(superior  cerebellar  peduncle);  cH,  fasciculus  tegmenti  centralis; C/'6,  corpus  pontobulbare 
(Essick) ;  Cr.?/,  corpus  restiforme;  Dca,  decussatio  cerebelli  anterior;  Dec/,  declive;  Emb, 
embolus  (nucleus  emboliformis);/c  Po,  fibraj  pontocerebellares;  Ffb,  fasciculus  fastigio- 
bulbaris  (uncinate  bunrlle  of  Russell); //,s/,  pedunculus  flocculi;  ,?/o&,  nucleus  globosus; 
Lm,  Lemniscus  medialis  (mesial  fillet  tract);  NVII,  nucleus  facialis  (motor  nucleus 
of  facial  nerve);  NaB,  nucleus  angularis,  or  superior,  vestibularis  (Bechterew);  Ndt, 
nucleus  dentatus  cerebelli;  Nod,  nodulus  cerebelli;  Nos,  nucleus  olivaris  superior; 
Nrl,  nucleus  reticularis  lateralis  (nucleus  of  the  lateral  column);  Nrtg,  nucleus 
reticularis  tegmenti;  Nt,  nucleus  tecti  (nucleus  fastigii);  Nvm,  nucleus  vestibularis 
magnocellularis  or  lateralis  (Deiters)  (large-celled  nucleus  of  vestibular  nerve);  Plchl, 
plexus  chorioideus  lateralis; /-"o,  pons;7-'y,  pyramid;5'/n,  stratum  intermedium  (pedunculi); 
Tr,  corpus  trapezoides;  vIV,  ventriculus  quartus;  vNdt,  vellus  nuclei  dentati  cerebelli 
(fleece  of  the  cerebellar  olive). 


THE  NERVOUS  SYSTEM.  447 

medial  lemniscus  or  form  an  independent  ascending  tract  in  the  reticular  forma- 
tion. The  fillet  is  about  the  same.  The  ventral  spino-cerebellar  and  spino-thal- 
amic  tracts  are  in  the  same  positions. 

Other  Afferent  Cerebellar  Neurones. — The  olives  are  still  larger  and  send 
many  bundles  of  olivo-cerebellar  fibres  to  the  opposite  restiform  body  which  has 
still  further  increased  in  size.  External  arcuate  fibres  may  be  present  and  probably 
contain  fibres  to  the  restiform  body  and  possibly  fibres  from  the  cerebellum,  which 
end  in  the  reticular  formation.  The  arcuate  nuclei  are  present.  The  central 
tegmental  tract  is  larger. 

Intersegmental  Neurones. — The  reticular  formation  is  very  extended.  Its 
composition  (longitudinal  and  transverse  fibres,  and  cells)  should  be  examined  care- 
fully. The  rubro-spinal  tract  is  in  the  same  position,  but  the  lateral  tract  from 
Deiters'  nucleus  is  now  more  internally  located.  Its  fibres  cannot  usually  be  dis- 
tinguished, but  are  bending  inward  and  toward  its  nucleus  of  origin  (located  some- 
what higher).  The  medial  longitudinal  fasciculus  may  be  partially  separated  from 
the  medial  lemniscus.  It  is  a  complex  bundle  and  contains  at  various  levels  (a) 
descending  and  ascending  fibres  from  Deiters'  nucleus  and  other  cells  scattered  in 
the  reticular  formation,  (b)  descending  fibres  from  the  interstitial  nucleus  of  Cajal 
in  the  tegmentum  of  the  midbrain,  (c)  according  to  some  recent  observations, 
descending  fibres  from  the  thalamus  which  end  in  the  nuclei  of  cranial  nerves  V,  VI, 
VIII  and  X.  The  fibres  of  this  fasciculus  probably  terminate  in  many  nuclei, 
especially  those  of  eye-muscle  nerves  (III,  IV  and  VI)  (comp.  Figs.  302,  308  and 
320). 

Efferent  Suprasegmental  Neurones. — The  pyramids  and  tecto-spinal  tracts 
are  in  the  same  positions.  The  aberrant  efferent  pallial  fibres  already  noted 
(p.  439)  may  be  seen  in  the  lemniscus. 

6.  Section  through  the  Hindbrain  at  Level  of  Junction  of  Pons  and  Cere- 
bellum and  Entrance  of  Vestibular  Nerve.     (Figs.  295  and  303.) 

The  most  conspicuous  features  are  the  nuclei  and  fibres  of  the  pons,  added 
ventrally  to  the  preceding  structures,  which  are  now  collectively  known  as  the 
tegmentum;  the  cerebellum,  enclosing  dorsally  the  foiirth  ventricle;  and  the  connec- 
tions {inferior  and  middle  peduncles,  arms,  or  brachia)  of  the  cerebellum  with  the 
rest  of  the  brain.  The  greater  part  (restiform  body)  of  the  inferior  peduncle 
represents  ascending  cerebellar  connections  from  all  parts  below  the  level,  the 
middle  peduncle  (from  the  pons)  represents  a  descending  connection  from  the 
pallium  to  the  cerebellum.  The  superior  peduncle  (eft'erent  cerebellar)  is  not  fully 
formed  at  this  level.     (Comp.  p.  455.) 

Efferent  Peripheral  Neurones. — In  this  level  and  that  of  the  next  section  are 
present  the  nuclei  and  root  fibres  of  nerves  VII  and  VI. 

The  nucleus  of  nerve  VII,  or  nucleus  facialis  is  seen  occupying  a  lateral  posi- 
tion in  the  reticular  formation  similar  to  that  of  the  nucleus  ambiguus.  In  it  may 
be  made  out  the  usual  plexus  of  fine  terminals  and  the  coarser  root  fibres  which 
proceed  dorso-mesially  to  the  floor  of  the  ventricle,  where  they  partially  envelop 
the  nucleus  of  the  VI  (usually  not  present  in  this  level).  They  then  turn  brainward, 
forming  a  compact  longitudinal   bundle   (next  section)   and   finallv  turn   ventre- 


44S 


THE  ORGANS. 


i/entr  z/' 


laterally  and  caudally  to  emerge  on  the  lateral  aspect.  This  latter  part  is  the  second 
part  as  distinguished  from  the  first  part  of  the  connection.  The  bend  is  known  as 
the  genu  facialis. 

Four  groups  of  cells  composing  the  nucleus  facialis  have  been  distinguished: 
three  ventral  groups  which,  passing  from  the  most  mesial  to  the  most  lateral 
group,  innervate  respectively  the  muscles  of  tympanum,  of  pinna  and  of  mouth 
and  face.     The  dorsal  group  (to  superior  branch  of  facial)  innervates  the  frontalis, 

corrugator  supercilii  and  orbicularis 
palpebrarum.  Among  the  terminals 
in  the  nucleus  have  been  distinguished 
collaterals  (reflex)  from  the  fillet, 
secondary  acoustic  and  trigeminal 
tracts  and  other  adjacent  fibres;  also 
terminals  of  the  tecto-spinal  tract. 
Whether  the  nucleus  receives  direct 
terminals  from  the  pyramids  or 
whether  fibres  of  the  latter  are  only 
connected  with  it  via  intercalated 
neurones  is  uncertain. 

Some  of  the  root  fibres  of  the  VI 
are  usually  seen  passing  to  the  surface. 
For  nucleus  see  next  section. 

Afferent  Roots,  their  Terminal 
Nuclei  and  Secondary  Tracts. — The 
afferent  vestibular  root  fibres  enter  at 
the  lower  border  of  the  pons  and  pass 
lateral  to  the  spinal  V,  mesial  to  the 
ventral  cochlear  nucleus  and  restiform 
body,  and  enter  the  field  previously 
occupied  by  the  descending  vestibular 
root,  the  fibres  of  which  are  a  con- 
tinuation of  the  root.  Scattered  large 
cells  in  this  region  form  the  nucleus  of 


A'/Z/t 


Fig.  304. — Diagram  of  Origin  of  Sixth  and 

Seventh  Cranial  Nerves.     (Schafer.)     pyr, 

Pyramid;  or,  restiform  body;  dV,  spinal  root 

of  fifth  nerve;  Ventr.  IV,  fourth  ventricle; 

VIII. V,    vestibular   root   of  eighth  nerve; 

n.VI,  chief  nucleus  of  sixth  nerve;  n'VI, 

accessory  nucleus  of  sixth  nerve;  VI,  sixth 

nerve;    n.VI  I,   nucleus   of   seventh    nerve, 

from  which  the  axones  pass  dorso-mesially 

to  the  floor  of  the  ventricle,  where  they  turn 

brainward,  appearing  as  a  bundle  of  trans- 
versely cut   fibres,    aVII,   and  ascend  to 

the  "genu,"  g,  where  they  turn  and  pass 

ventro-laterally  and  somewhat  caudally  to 

the  surface  as  the  seventh  nerve,  VII. 

Deitcrs.  Dorso-mesial  to  this  is  still 
the  medial  vestibular  terminal  nucleus  and  dorsal  to  Deiters'  at  the  external  angle 
of  the  fourth  ventricle  is  the  .superior  vestibular  terminal  nucleus  (von  Bechterew). 
Fibres  seen  passing  from  the  vestibular  region  to  the  cerebellum  and  lying  near 
the  ventricle  are  partly  vestibular  root  fibres  to  the  cerebellum  (especially  to  the 
nucleus  tecti,  or  fa.stigii,  .see  below),  and  partly  descending  fibres  from  cerebellar 
nuclei  (especially  from  the  nuclei  fa.stigii,  iorm'ing  fastigio-bulbar  fibres)  to  Deiters' 
nucleus,  other  vestibular  nuclei,  and  other  cells  in  the  reticular  formation.  It 
is  thus  evident  that  such  nuclei  as  Deiters'  may  act  as  parts  of  vestibular  bulbo- 
spinal reflex  arcs  and  also  as  parts  of  efferent  cerebellar  paths.  Internal  arcuate 
fibres  from  the  vestibular  area  are  probably  princij)ally  fibres  (.secondary  tracts) 
from  the  various  vestibular  nuclei  to  the  medial  longitudinal  fasciculus  and  other 
tracts  in  the  reticular  formation.  (Comp.  pp.  441,  449,  455,  Figs.  302,  308.) 
The  nucleus  olivaris  .superior  lies  ventral  to  the  nucleus  facialis  and  lateral 


THE  NERVOUS  SYSTEM.  449 

to  the  central  tegmental  tract.  This  nucleus  together  with  several  other  small 
nuclei  in  its  immediate  vicinity  (preolivary  nucleus,  semilunar  nucleus,  trapezoid  nu- 
cleus) is  one  of  the  nuclei  intercalated  in  the  cochlear  path  (Fig.  301).  Lateral 
to  it  is  seen  a  mass  of  fibres  which  pass  by  it  toward  the  median  line  through  the 
medial  lemniscus,  and  decussate,  finally  turning  longitudinally  dorso-lateral  to 
the  opposite  superior  olive.  These  are  fibres  of  the  trapezius,  and  together  with  the 
more  dorsal  secondary  cochlear  fibres  (p.  441)  form  the  lateral  lemniscus  (See  Fig. 
301  and  page  441).  The  lateral  lemniscus  is  thus  one  of  the  links  in  the  cochlear 
or  auditory  pathway.  Fibres  pass  from  superior  olive  to  nucleus  of  nerve  \T 
(reflex).      (For  the  afferent  part  of  VII,  see  Table  of  Cranial  Nerves.) 

The  spinal  V  occupies  the  same  position  though  separated  from  the  surface  by 
the  pontile  fibres;  internal  to  it  is  its  terminal  nucleus.  Note  the  change  in  the 
shape  of  the  lemniscus.  The  ventral  spino-cerebellar  and  spino-thalamic  tracts 
are  in  the  same  position  though  separated  from  the  surface  by  the  mass  of  pontile 
fibres. 

Other  Afferent  Cerebellar  Neurones. — The  inferior  olives  are  not  present,  and 
the  olivo-cerebellar  fibres  are  here  entering  the  cerebellum  as  a  part  of  the  restiform 
body.  The  central  tegmental  tract  (to  the  olives)  occupies  the  ventral  part  of  the 
reticular  formation.  The  restiform  body  is  entering  the  white  matter  of  the  cere- 
bellum. It  has  been  seen  to  be  composed  of  the  dorsal  spino-cerebellar  tract, 
olivo-cerebellar  fibres  and  fibres  from  the  lateral  and  possibly  other  nuclei  in  the 
reticular  formation.  The  dorsal  spino-cerebellar  tract  terminates  in  the  cortex 
of  the  vermis  or  middle  lobe  of  the  cerebellum,  the  olivo-cerebellar  fibres  terminate 
in  all  parts  of  the  cerebellar  cortex.  The  fibres  mesial  to  the  restiform  body, 
consisting  of  ascending  vestibular  fibres  to  the  cerebellum  and  descending  fibres  to 
vestibular  and  other  nuclei  (see  cerebellum),  are  sometimes  called  the  internal  or 
juxta-restiform  body.  This  and  the  restiform  body  proper  constitute  the  inferior 
cerebellar  peduncle.  The  pons  consists  of  gray  matter — the  pontile  nuclei — and  of 
transverse  and  longitudinal  fibres.  The  longitudinal  fibres  include  the  pyramids 
which  pass  through  to  the  medulla  and  cord,  and  other  fibres  from  the  pallium 
(pallio-pontile  or  cerebro-pontile)  which  terminate  in  the  pontile  nuclei.  The 
axones  of  the  latter  form  the  transverse  pontile  fibres  (ponto-cerebellar  fibres) 
which  cross  and  pass  to  the  cortex  of  the  opposite  cerebellar  hemisphere.  They 
constitute  the  middle  cerebellar  peduncle  or  brachium  pontis.     (Comp.  p.  455.) 

This  whole  pontile  system  may  be  termed  the  pallio-cerebellar  path  or  con- 
nection. It  is  principally,  or  entirely,  a  crossed  connection.  There  are  prob- 
ably also  transverse  fibres  in  the  pons  connecting  cerebellum  and  reticular  forma- 
tion. Fibres  passing  vertically  in  the  raphe  from  pons  to  reticular  formation 
{perpendicular  -fibres  of  pons)  may  be  in  part  continuations  of  these  and  in  part 
efferent  pallial  fibres  from  pes  to  tegmentum.  The  latter  are  either  aberrant 
fibres  or  fibres  innervating  directly  or  indirectly  motor  cranial  nuclei. 

Intersegmental  Neurones. — The  reticular  formation  is  e.xtensive.  In  it  there 
may  be  distinguished,  besides  the  nuclei  already  mentioned,  various  more  or  less 
well-defined  reticular  nuclei  (see  Fig.  303).  The  fibres  of  the  lateral  tract  from 
Deiters'  nucleus  (not  distinguishable)  are  here  emerging  from  Deitcrs'  nucleus. 
The  medial  longitudinal  fasciculus  occupies  the  same  position,  but  is  here  well 
separated  from  the  fillet.  Some  of  the  internal  arcuate  fibres  in  the  dorsal  part  of 
29 


450  THE  ORGANS. 

the  reticular  formation  may  be  fibres  from  Deiters'  nucleus  to  this  bundle.  They 
may  be  crossed  or  uncrossed,  and  may  descend  in  it  as  already  mentioned  (page  418) 
or  ascend  (see  Fig.  302).  Other  internal  arcuate  fibres  here,  as  elsewhere,  pass  from 
the  various  terminal  nuclei  to  form  secondary  tracts.  Other  transverse  fibres  are 
axones  of  cells  of  reticular  nuclei  or  collaterals  and  terminals  ending  in  them. 

Efferent  Suprasegmental  Neurones. — The  spino-tectal  tract  lies  ventral 
to  the  medial  longitudinal  fasciculus.  The  pyramids  are  in  the  same  position,  but 
are  partly  surrounded  by  pontile  fibres  and  nuclei.     (See  also  pons,  above.) 

The  Cerebellum. — In  the  gray  matter  there  is  to  be  distinguished  the  external 
gray  or  cortex,  and  internal  nuclei  forming  interruptions  or  relays  in  paths  to  and 
from  the  cortex.  The  white  matter  consists  of  the  fibres  of  various  afferent  and 
efferent  cerebellar  paths  and  association  fibres  of  the  cerebellum.  The  cortex  is 
studied  elsewhere.  The  internal  nuclei  can  usually  be  distinguished.  They  are 
the  nucleus  dentatus  cerebelli  {corpus  dentatum),  a  convoluted  mass  of  gray  resembling 
the  inferior  olives  (and  sometimes  called  the  cerebellar  olives),  and  mesial  to  this 
the  nucleus  globosus,  nucleus  emboliformis  and  the  nucleus  tecli  or  fastigii.  The 
nucleus  tecti  receives  fibres  from  various  parts  of  the  cerebellar  cortex  and  also 
vestibular  root  fibres  (p.  445).  Its  axones,  in  part  at  least,  pass  to  Deiters'  nucleus  and 
other  nuclei  in  the  reticular  formation  {fastigio-bulbar  tract).  The  corpus  den- 
tatum, nucleus  globosus,  and  nucleus  emboliformis  also  receive  fibres  from  the 
cerebellar  cortex.  Their  axones  form  the  superior  cerebellar  peduncle  (brachium 
confunctivum),  cross  and  pass  to  the  red  nucleus,  reticular  formation,  nucleus  of 
nerve  III,  and  thalamus.  At  the  level  of  the  section  the  superior  peduncle  is  not 
yet  fully  formed.      (See  also  p.  445.) 

Note  where  possible  the  structure  of  the  plexus  chorioideus  of  the  fourth  ventricle. 
It  consists  of  a  layer  of  flattened  cells  next  the  ventricle  which  are  ectodermic, 
and  an  outer  mesodermic  part  consisting  of  connective  tissue  and  blood-vessels. 

7.  Transverse  Section  of  the  Hindbrain  through  the  Roots  of  Nerves  VI 
(Abducensj  and  VII  (Facial).     (Figs.  295  and  305.) 

Efferent  Peripheral  Neurones. — The  nucleus  facialis  is  usually  not  present 
but  various  portions  of  the  root  fibres  may  be  present  (see  preceding  section),  espe- 
cially the  longitudinal  part. 

The  nucleus  of  the  VI  or  nucleus  abducentis  is  present  in  about  the  middle  of  the 
floor  of  the  ventricle  and  just  beneath  the  central  gray  or  partly  within  it.  Its 
fibres,  the  root  fibres  0)  the  abducens,  are  seen  passing  ventrally. 

Afferent  Roots,  Their  Terminal  Nuclei  and  Secondary  Tracts. — The 
lateral  (Deiters')  and  medial  ve.stibular  nuclei  are  usually  still  present,  also  possibly 
fastigio-bulbar  fibres.  The  ventral  cochlear  nucleus  has  disappeared,  but  other 
cochlear  nuclei  (superior  olivary  and  trapezoid)  are  usually  present.  Often  fibres 
can  be  .seen  passing  from  the  superior  olive  to  the  nucleus  VI. 

Fibresof  the  secondary  cochlear  tract  (corpus  trapezoideum)  arc  still  traversing 
the  medial  lemniscus,  and  decussating.  The  tract  they  are  forming  (lateral 
lemniscus)  is  not  yet  very  distinct. 

The  spinal  V  is  in  the  same  position,  but  it  and  its  terminal  nucleus  tend  to 
separate  into  groups  of  fibres  and  cells,  and  to  change  their  relative  positions.     The 


THE  NER\'OUS  SYSTEM. 


451 


452  THE  ORGANS. 

medial  lemniscus  is  more  flattened  in  cross  section,  extending  transversely  instead 
of  dorso-ventrally.  The  ventral  spino-cerebellar  tract  and  spino-thalamic  tract 
are  in  the  same  positions  in  the  external  part  of  the  tegmentum  ventral  to  the  spinal 
V  and  external  to  the  superior  olive. 

Other  Afferent  Cerebellar  Connections. — The  restiform  body  has  now 
merged  with  the  white  matter  of  the  cerebellum.  The  nuclei  and  transverse  fibres 
of  the  pons  (ponto-cerebellar  neurones)  have  increased.  The  longitudinal  fibres  in 
the  pons  at  this  level  are  principally  the  pyramids,  but  some  are  pallio-pontile  fibres 
which  terminate  in  the  nuclei  pontis.     Perpendicular  fibres  are  present. 

Intersegmental  Neurones. — The  reticular  formation  is  practically  unchanged. 
One  of  its  nuclei  {nucleus  reticularis  tegmenti)  can  be  seen  as  a  lighter  area  (Weigert) 
in  the  medial  part,  dorsal  to  the  medial  lemniscus.  The  rubro-spinal  tract  is  in  the 
same  position  near  or  mingled  with  the  spino-thalamic  and  ventral  spino-cerebellar 
tracts.  These  fibres  are  not  easily  distinguished  among  the  various  fibres  of  the 
cochlear  tract  which  cross  them.  The  medial  longitudinal  fasciculus  is  now  a 
well-marked  tract  occupying  the  same  position.  From  now  on,  it  contains  ascend- 
ing fibres  from  Deiters'  nucleus  and  perhaps  other  reticular  nuclei  besides  the 
descending  fibres  from  the  interstitial  nucleus  of  Cajal. 

Efferent  Suprasegmental  Neurones. — The  pyramids  and  tecto-spinal  tract 
(predorsal  fasciculus)  occupy  the  same  positions.  The  fastigio-bulbar  fibres  have 
been  mentioned.  The  superior  cerebellar  peduncle  is  now  more  distinct  as  it  is 
being  formed  by  fibres  from  the  dentate  nucleus.  It  lies  near  the  dorso-lateral  part 
of  the  ventricle. 

8.  Transverse  Section  of   the  Hindbrain  Through  the  Roots  of  Nerve  V 
(Trigeminus).     (Figs.  295  and  306  ) 

Efferent  Peripheral  Neurones. — Motor  nucleus  of  V.  This  is  mesial  to  the 
terminal  nucleus  of  the  V  and  its  coarse  efferent  root  fibres  may  be  seen,  in  favor- 
able levels,  passing  out  with  the  entering  afferent  fibres.  Some  of  the  finer  ter- 
minal fibres  present  in  the  nucleus  are  afferent  root  fibres  of- the  V  (two-neurone 
arc)  and  collaterals  of  secondary  tracts  of  V  (three-neurone  arc)  The  nature 
of  its  connections  with  efferent  pallial  fibres  is  not  known.  Collaterals  are  also 
received  from  the  mesencephalic  root.      (Fig.  307.) 

Afferent  Roots,  their  Terminal  Nuclei  and  Secondary  Tracts. — The  af- 
ferent fibres  of  the  V  pa.ss  through  the  pons  and  enter  the  tegmentum  where  they 
divide  into  short  ascending  and  long  descending  arms.  The  former,  together  with 
collaterals,  terminate  in  the  cephalic  end  of  the  terminal  nucleus  of  the  V.  This 
is  broken  up  into  groups  of  cells  which  lie  dorso-lateral  to  the  entering  fibres. 
The  long  descending  arms  pass  down  to  the  cord  as  the  spinal  V,  giving  off  collat- 
erals and  terminals  to  the  terminal  nucleus  en  route.  (Fig.  307).  A  third  source  of 
fibres  of  the  V  is  a  series  of  cells  extending  upward  into  the  roof  of  the  mesencepha 
Ion.  The  axones  of  these  cells  form  the  mesencephalic  root  of  the  V.  There  is 
reason  to  suppose,  from  their  peculiar  location  and  for  other  reasons,  that  these 
are  afferent  pjeripheral  neurones  which  have  remained  within  the  neural  tube. 
From  the  region  of  the  terminal  nucleus  of  the  V,  a  transverse  bundle  passes  to  the 
opposite  side  in  the  floor  of  the  fourth  ventricle.     This  is  considered  a  secondary 


THE  NERVOUS  SYSTEM. 


453 


454 


THE  ORGANS. 


decussating  trigeminal  tract  which  forms  an  ascending  tract  in  the  dorsal  part  of 
the  reticular  formation.  Fibres  of  secondary  tracts  give  off  collaterals  to  various 
efferent  nuclei  and  probably  axones  of  some  cells  of  the  terminal  nuclei  become 
intersegmental  fibres  in  the  reticular  formation.  Secondary  tracts  to  the  thal- 
amus {via  fillet  and  also  in  reticular  formation?)  form  part  of  the  trigeminal 
afferent  palHal  path. 

The  superior  terminal  vestibular  nucleus  (of  von  Bechterew)  may  still  be  present. 
The  superior  olivary  and  trapezoid  nuclei  may  be  present.     The  secondary  (and 


Fig.  307. — Diagram  of  Origin  of  Fifth  Cranial  Nerve.  (Schafer.)  G,  Gasserian 
ganglion;  a,b,c,  the  three  divisions  of  the  nerve;  m.n.V,  principal  motor  nucleus;  p.s.n.V, 
principal  terminal  "sensory "  nucleus;  d.s.n.V,  terminal  nucleus  of  spinal  root;  d.s.V, 
descending  or  spinal  root;  c.V  and  c'.V,  secondary  trigeminal  tracts  (axones  of  cells  in 
terminal  nuclei);  r,  median  raphe;  m'.n.V,  mesencephalic  nucleus. 


tertiary  (?),  see  Fig.  301)  cochlear  tract  or  lateral  lemniscus  is  now  well  formed  and 
may  be  seen  lying  dorsodateral  to  the  superior  olivary  and  trapezoid  nuclei. 

The  medial  lemniscus  is  still  more  flattened.  The  spino-thalamic  and  ventral 
spino-corcbeJlar  tracts  occupy  the  same  positions. 

Other  Afferent  Cerebellar  Neurones.  4'he  transverse  pons  fibres  are  the  same, 
but  the  longitudinal  fibres  have  increased  owing  to  the  presence  of  more  pallio- 
pontile  fibres.  The  perpendicular  pontile  fibres  are  seen  passing  dorsally  in 
the  raphe  into  the  tegmentum. 

The  central  tegmental  tract  is  in  nearly  the  same  position. 

Intersegmental  Neurones.  -  The  reticular  formation  is  somewhat  diminished. 
In  it  is  the  nucleus  reticularis  tegmenti.  The  rubro-spinal  tract  is  in  the  same 
position,  mingled  with  the  spino-thalamic  and  ventral  spino-cerebellar.  The 
medial  longitudinal  fasciculus  is  unchanged. 


THE  NERVOUS  SYSTEM.  455 

Efferent  Suprasegmental  Neurones. — The  pyramids  now  occupy  the  central 
part  of  the  pons,  and  are  broken  up  into  a  number  of  bundles.  In  the  dorsal  part 
of,  the  pons  fibres  pass  obliquely  dorsally.  These  are  probably  efferent  pallial  fibres 
which  act  directly  or  indirectly  on  some  of  the  efferent  nuclei  of  cranial  nerves 
(motor  path  to  cranial  nerves).     The  pallio-pontile  fibres  have  been  mentioned. 

The  superior  peduncle  is  now  a  large  bundle  of  fibres  flattened  against  the  inner 
surface  of  the  dorso-lateral  brain  wall. 

The  tecto-spinal  tract  is  in  the  same  position. 

Cerebellum. 

The  cerebellum,  connected  with  the  rest  of  the  brain  by  its  three 
peduncles,  consists  of  two  lateral  lobes  or  hemispheres  connected  by  a 
median  lobe,  the  vermis.  These  are  divided  into  various  lobules,  the 
surfaces  of  which  are  marked  by  parallel  transverse  folds  or  laminae. 
When  these  are  cut  across  it  is  seen  that  they  give  off  secondary  or 
tertiary  laminae,  the  whole  producing  the  appearance  known  as  the 
arbor  vitae.  The  surface  of  the  cerebellum  is  composed  of  gray  matter, 
the  cortex,  enveloping  the  white  matter.  Besides  this  there  are  masses 
of  gray  within,  the  internal  nuclei  of  the  cerebellum  (dentatus,  globosus 
emboliformis,  and  fastigii),  embedded  in  its  white  matter.  Fibres 
entering  the  cortex  are  the  terminations  of  the  fibres  of  the  restiform 
body  (dorsal  spino-cerebellar  tract  to  the  cortex  of  the  vermis, 
olivo-cerebellar  fibres  to  the  whole  cortex,  fibres  from  the  lateral  nucleus 
and  possibly  other  nuclei  in  the  reticular  formation),  vestibular  root 
fibres  to  the  vermis,  the  ventral  spino-cerebellar  tract  to  the  vermis, 
and  the  pontile  fibres  to  the  cortex  of  the  hemispheres.  The  cortical 
cells  do  not  send  axones  outside  the  cerebellum,  all  efferent  fibres 
being  interrupted  in  the  internal  nuclei.  The  dentate  nucleus  receives 
fibres  from  the  cortex  of  the  hemispheres;  the  globose  and  emboliform 
nuclei  receive  fibres  from  the  cortex  of  the  vermis;  and  the  nucleus 
fastigii  receives  fibres  from  various  parts.  The  axones  of  the  first 
three  form  the  superior  peduncle;  the  axones  of  the  nucleus  fastigii 
are  fastigio-bulbar  fibres,  principally  crossed,  to  vestibular  nuclei  and 
possibly  other  reticular  formation  nuclei.  There  may  be  some  eft'er- 
ent  fibres  in  the  middle  peduncle  to  reticular  formation  nuclei,  but  the 
major  part,  at  least,  of  this  peduncle  consists  of  the  ponto-cerebellar 
fibres  already  described.  The  inferior  and  middle  peduncles  are  thus 
largely  afferent  and  the  superior  peduncle  is  efferent,  to  red  nucleus, 
thalamus  and  nucleus  of  nerve  III.      (Figs.  294  and  308.) 

In  the  cortex  can  be  distinguished  an  outer  or  molecular  layer  with 
few  cells  and  few  medullated  fibres,  an  inner,  ^^raniilar  or  unclear  layer. 


456 


THE  ORGANS. 


and  between  the  two  a  single  row  of  large  flask-shaped  cells,  the  cells 
of  Piii'kinje  (Figs.  309,  310).  These  latter  give  off  several  main  den- 
drites, which  enter  the  molecular  layer  and  form  a  remarkably  rich 
arborization  extending  to  the  surface.  The  Golgi  method  shows  the 
larger  and  medium  branches  smooth,  but  the  terminal  branches  thickly 
beset  with  "gemmules."  The  dendritic  arborization  is  flattened,  ex- 
tending at  right  angles  to  the  laminae.  The  axone  is  given  off  from  the 
end  opposite  to  the  dendrites  and  passes  through  the  granular  layer 


Fig.  309. — Part  of  a  Vertical  Section  through  the  Aduh  Human  Cerebellar  Cortex. 
Nissl  Method.  (Cajal).  A,  Inner  portion  of  the  molecular  layer;  B,  granular  layer;  C, 
body  of  a  Purkinje  cell;  a,  stellate  cell  of  the  molecular  layer;  b,  nuclei  of  the  epithelial-like 
neuroglia  cells  (cells  of  the  fibres  of  Bergmann);  c,  stellate  cell  with  marginal  chromophilic 
substance;  d,  fibrillar  mass  corresponding  to  the  baskets;  e,  nuclei  of  the  granule  cells; 
/,  islands  or  glomeruli  in  the  granular  layer;  g,  h,  Golgi  cells  in  the  granular  layer;  i,  nuclei  of 
neuroglia  cells. 

into  the  white  matter,  either  to  one  of  the  internal  cerebellar  nuclei 
where  it  terminates,  or  to  some  other  part  of  the  cortex.  The  Purkinje 
cells  are  almost  the  only  cells,  the  axones  of  which  enter  the  white 
matter.  It  is  evident  that  all  intracortical  connections  must  ultimately 
converge  on  these  cells  to  reach  the  efferent  cerebellar  paths.  The 
axones  of  the  Purkinje  cells  give  off  collaterals  not  far  from  their  origin, 
which  pass  into  the  molecular  layer  and  appear  to  terminate  there  in 
end  "buttons"  upon  the  bodies  of  adjacent  Purkinje  cells.  The  med- 
ullated  axones  form  the  coarser  fibres  traversing  the  granular  layer. 
The  cell  body  is  fairly  well  filled  with  small  chromophilic  bodies  of 


THE  XER\'OUS  SYSTEM.  457 

uniform    size,    often     showing    a    slightly    concentric    arrangement 
(Fig.  309). 

The  cells  in  the  molecular  layer  (stellate  cells)  are  either  superficial 
stellate  cells  with  irregular  branching  dendrites  and  a  short  axone  or 
deep  stellate  (basket)  cells.  These  latter  are  cells  the  axones  of  which 
(apparently  non-medullated)  have  a  narrow  neck  and  unusual  thicken- 
ing beyond  the  neck.  They  extend  at  right  angles  to  the  laminae  for 
a  distance  of  several  Purkinje  cells,  giving  off  to  each  Purkinje  cell  one 
or  more  collaterals  which  pass  toward  the  granular  layer  and  envelop. 


Fig.  310. — Purkinje  Cell  of  .\dult  Human  Cerebellum.  Golgi  preparation.  (Cajal.j 
a,  Axone;  b,  recurrent  collateral;  d,  spaces  occupied  by  basket  cells;  c,  spaces  occupied  bv 
blood-vessels. 

with  their  terminal  arborizations,  the  body  and  proximal,  non- 
medullated  portion  of  the  axone  of  the  Purkinje  cell.  Collaterals  of 
other  basket  cell  axones  may  terminate  around  the  same  Purkinje  cell, 
forming  the  ''basket."  The  dendrites  of  the  basket  cells  ramify 
throughout  the  molecular  layer.  Besides  the  cells  contained  in  it,  and 
the  dendritic  arborizations  of  the  Purkinje  cells,  the  molecular  layer 
contains  the  axones  of  the  granule  cells  and  the  terminations  of  the 
climbing  libres  (see  below) .  In  ordinary  stains  it  presents  a  general  punc- 
tate appearance,  with  the  scattered  nuclei  of  the  short  axone  and  basket 


458 


THE  ORGANS. 


cells,  and  the  coarser  dendrites  of  the  Purkinje  cells  distinguishable. 
(Figs.  309  and  311.) 

The  granular  layer  with  ordinary  stains  presents  the  appearance  of 
closely  packed  nuclei  with  clear  spaces  here  and  there  ("islands^^  or 
'' glomeridV^)  and  also  a  few  larger  cells  (Fig.  309).  Most  of  these 
nuclei  belong  to  the  granule  cells,  which  are  caryochrome  cells.  The 
granule  cells  are  sm.all  and  possess  three  to  six  dendrites  which  are 
comparatively  short  and  terminate  in  the  glomeruli  with  a  compact 
arborization,  each  branch  of  which  ends  in  a  small  varicosity.     The 


Fig.  311. — Section  of  Adult  Human  Cerebellum.  Silver  Method  of  Cajal.  (Cajal.) 
A,  B,  Cells  in  the  granular  layer  enveloped  by  basket  fibres;  C,  cell  of  Purkinje.  The 
axone  of  one  of  the  cells  of  Purkinje  is  shown. 


axones  of  the  granule  cells,  which  are  non-medullated,  ascend  into 
the  molecular  layer  where  each  divides  into  two  branches  running  longi- 
tudinally along  the  laminae,  and  terminating  in  v^aricosities  (Figs.  312, 
314).  These  are  the  parallel  fibres  of  the  molecular  layer.  They 
thus  run  at  right  angles  to  and  through  the  dendritic  expansions  of 
the  Purkinje  cells  and  their  cross  sections  together  with  the  terminal 
dendritic  arborizations  of  the  Purkinje  cells  give  the  molecular  layer 
its  punctate  appearance.  The  scattered  larger  cells  in  the  granular 
layer  are  ijrinci[jally  short  axone  or  Gc/,1^''/ cf//.v,  whose  main  dendrites 
usually  [penetrate  and  branch  within  the  molecular  layer.  Their  axones 
often  form  very  extensive  and  com.plicated  arborizations  in  the  granular 
layer,  the  terminations  of  which  are  concentrated  in   the  glomeruli. 


THE  NERVOUS  SYSTEM. 


459 


Fig.  312. — Diagram  of  Longitudinal  Section  of  Cerebellar  Lamina.  Golgi  method. 
(Kolliker.)  gr.  Cell  of  the  granular  layer;  n,  axone  of  granule  cell ;  «',  the  same  in  molecular 
layer  where  it  branches  and  runs  in  long  axis  of  lamina;  p,  Fuvk'mje  cell  showing  how- 
much  less  extensively  its  dendrites  (p')  branch  in  long  axis  of  lamina.     (Compare  Fig.  314.) 


Fig.  313. — Granule  Cells  and  IMossy  Fibres  in  the  Cerebellum  of  Adult  Cat.  Silver 
method  of  Cajal.  (Cajal.)  .4,  Granule  cell;  B,  Golgi  cell;  a,  dendritic  arborization  of 
granule  cell;  b,  mossy  fibres  passing  by  Golgi  cell;  c,  mossy  fibre;  d,  termination  of  a 
mossy  fibre;  e,  terminal  processes  given  off  from  a  thickening  in  a  mossy  fibre. 


460 


THE  ORGANS. 


Dislocated  cells  of  this  type  may  have  their  cell  bodies  in  the  molecular 
layer. 

In  the  cortex  there  are  also  the  terminations  of  the  afferent  cerebellar 
fibres  already  mentioned  (p.  455).  These  are  of  two  types,  mossy 
fibres  and  climbing  fibres.  The  mossy  fibres,  so  called  from  the  appear- 
ance of  their  terminations  in  embryos,  are  the  coarsest  fibres  of  the 
white  matter.     While  in  the  latter  they  bifurcate,  branches  going  to 


Fig.  314. — Semi-diagrammatic  transverse  Section  of  a  Cerebellar  Lamina  of  a  Mam- 
mal, as  shown  by  the  Golgi  Method.  (Cajal.)  A,  Molecular  layer;  B,  granular  layer; 
C,  white  matter;  a,  Purkinje  cell,  seen  flat;  b,  basket  cells  of  the  molecular  layer;  d,  their 
terminal  arborizations  which  envelop  the  bodies  of  the  Purkinje  cells;  e,  superficial  stellate 
cells;/,  Golgi  cell;  g,  granule  cells  with  their  axis-cylinders  ascending  and  bifurcating  at  i; 
h,  inossy  fibres;  j,  neuroglia  cell;  m,  neuroglia  cell  in  granular  layer;  n,  climbing  fibres. 

different  laminae.  These  main  branches  give  off  secondary  branches 
which  enter  the  granular  layer  and  there  arborize.  During  their  course, 
and  also  at  their  terminations,  these  branches  arc  thickened  in  places 
and  there  give  off  short,  thick,  terminal  branches  which  end  in  varicosi- 
ties. These  terminal  branches  are  located  within  the  glomeruli.  The 
glomeruli  thus  contain  the  dendritic  terminations  of  the  granule  cells, 
the  axonal  terminations  of  the  Golgi  cells,  and  the  terminations  of  the 
mos.sy  fibres.      (Fig.  313.) 


THE  NERVOUS  SYSTEM. 


461 


The  climbing  fibres  pass  from  the  white  matter,  through  the  granular 
layer  to  the  cells  of  Purkinje.  Passing  by  the  bodies  of  the  latter  they 
arborize  into  terminals  which  envelop  the  smooth  dendritic  branches 
of  the  Purkinje  cells;  i.e.,  all  but  the  terminal  dendritic  arborizations. 
Three  kinds  of  fibres  thus  terminate  around  the  Purkinje  cells;  the 
granule  axones,  probably  in  contact  with  its  terminal  dendritic  arboriza- 
tions; the  climbing  fibres  around  its  coarser  dendritic  branches;  and  the 
basket  fibres  around  its  body.  The  respective  sources  of  the  mossy  and 
climbing  fibres  are  unknown. 


Fig.  315. — Cross  Section  of  a  Cerebellar  Convolution  Stained  by  Weigert's  ISIethod. 
(Kolliker.)  m,  Molecular  layer;  K,  granular  layer;  ti',  white  matter;  q,  fine  fibres  passing 
from  white  matter  into  the  molecular  layer;  tr,  dots  represent  longitudinal  fibres  of  molecular 
layer  among  bodies  of  Purkinje  cells. 


It  is  evident  from  the  above  that  all  of  the  cells  of  the  cerebellar 
cortex  except  the  Purkinje  cells  are  association  cells  of  the  cortex. 

The  medullated  fibres  of  the  cerebellum  (Weigert)  (Fig.  315)  pass 
from  the  white  matter  into  the  granular  layer  and  ramify  throughout 
the  latter,  forming  quite  a  dense  plexus  separating  groups  of  granule 
cells.  Sometimes  straight  fibres  can  be  seen  passing  through  toward 
the  molecular  layer  which  are  probably  either  the  climbing  fibres  or 
axones  of  the  Purkinje  cells.  Beneath  and  between  the  bodies  of  the 
Purkinje  cells  is  a  plexus  of  fibres  extending  into  the  deeper  j^art  of 
the  molecular  layer,  the  remainder  of  this  layer  containing  few  or  no 


462  THE  ORGANS. 

medullated  fibres.  These  fibres  in  the  vicinity  of  the  Purkinje  cells 
are  probably  principally  formed  by  the  recurrent  collaterals  of  the 
Purkinje  cells  already  mentioned.  The  remaining  fibres  of  the 
granular  plexus  would  apparently  consist  of  the  arborizations  of  mossy 
fibres  and  of  the  Golgi  cells.  Whether  the  former  are  medullated  is, 
however,  somewhat  uncertain. 

Most  of  the  neuroglia  cells  in  the  cerebellum  are  of  the  same  general 
type  as  seen  elsewhere,  but  in  the  Purkinje  cell  layer  are  apparently 
epithelial-like  cells  which  send  vertical  processes  to  the  periphery. 
Some  of  these  processes,  as  seen  in  the  Golgi  method,  are  rough  and 
branched,  others  are  smooth.  In  ordinary  stains  these  processes  are 
sometimes  visible  and  are  known  as  the  fibres  of  Bergmann.  (Figs.  309, 
314-) 

Isthmus. 

PRACTICAL  STUDY. 

9.   Transverse   Section   through   the   Isthmus   at   the  Exit   of    Nerve    IV 
(Trochlearis).     (Figs.  295  and  316.) 

In  this  there  are  to  be  distinguished  three  parts,  the  thin  roof  (superior  medul- 
lary velum),  the  tegmentum  and,  ventral  to  the  latter,  the  pons.  The  tegmentum 
consists  essentially  of  the  reticular  formation,  efferent  cerebellar  and  midbrain 
connections,  and  externally  the  afferent  pallial  connections.  The  pons  contains 
the  efferent  pallial  paths  to  the  cerebellum  and  parts  of  the  nervous  system  caudal 
to  it.  The  cavity  is  the  iter  or  aqueductus  Sylvii.  Next  to  this  is  the  central  gray 
of  the  brain  wall. 

Efferent  Peripheral  Neurones. — The  root  fibres  of  the  IV  are  seen  in  the  roof. 
They  originate  from  nuclei  lying  further  forward  in  the  ventral  part  of  the  central 
gray.  The  fibres  pass  from  the  nuclei  dorsally  and  caudally  in  the  outer  part  of  the 
central  gray  and  finally  decussate  in  the  roof  and  emerge.  It  is  only  the  latter  part 
of  this  course  which  is  seen  in  this  level. 

Afferent  Roots,  their  Terminal  Nuclei  and  Secondary  Tracts. — The  mesen- 
cejjhalic  root  of  the  V  lies  in  the  lateral  part  of  the  central  gray.  Mingled  with  its 
fibres  may  be  seen  the  rounded  cells,  the  axones  of  which  form  these  fibres. 

The  lateral  lemniscus  occupies  part  of  the  lateral  swelling  on  the  surface  of  the 
tegmentum.  Groups  of  cells  among  its  fibres  constitute  the  dorsal  nucleus  of  the 
lateral  lemniscus.  The  medial  lemniscus  is  now  still  more  flattened.  The  spino- 
thalamic tract  is  in  about  the  same  position,  l^etween  the  two  lemnisci.  At  this 
level,  the  principal  afferent  supra.segmental  paths  form  an  L-shaped  mass,  envelop- 
ing the  rest  of  the  tegmentum  and  representing  general  bodily  sensation  and  hear- 
ing. There  are  also  cranial  nerve  ascending  paths  lying  probably  within  the  retic- 
ular formation  and  fillet  (secondary  vago-g!o.ssopharyngeal  and  trigeminal  tracts, 
repre.senting  visceral,  taste,  and  general  head  sensation).  These  cannot  be  distin- 
guished in  the  section. 


THE  NERVOUS  SYSTEM. 


463 


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464  THE  ORGANS. 

The  ventral  spino-cerebellar  tract  is  on  the  surface,  and  now  comes  to  lie  exter- 
nal to  the  superior  cerebellar  peduncle.  At  about  this  point  it  turns  caudally, 
and  passes  back  into  the  cerebellum,  accompanying  the  superior  peduncle. 

Other  Afferent  Cerebellar  Connections. — The  central  tegmental  tract  oc- 
cupies the  same  position.  (For  the  pallio-cerebellar  connection  see  "Efferent 
Suprasegmental  Neurones"  below.) 

Intersegmental  Neurones. — The  reticular  formation  is  diminished  in  extent. 
One  of  its  nuclei,  the  nucleus  centralis  superior,  lies  near  the  raphe.  The  rubro- 
spinal tract  has  moved  somewhat  mesially.  It  is  dorsal  to  the  medial  lemniscus. 
The  medial  longitudinal  fasciculus  is  in  the  same  position,  and  is  a  well-marked 
bundle  lying  at  the  boundary  between  the  ventral  part  of  the  central  gray  and  the 
reticular  formation. 

Efferent  Suprasegmental  Neurones. — The  pyramids  are  now  broken  up  into 
bundles  which  may  show  a  tendency  to  gather  in  the  ventral  part  of  the  pons 
(distinguishable  in  one-month  infant,  where  they  are  medullated  while  the  pontile 
system  is  not).  Bundles  apparently  forming  lateral  and  mesial  portions  of  the 
medial  lemniscus  (not  indicated  in  the  figure)  are  aberrant  efferent  pallial  fibres. 
Such  bundles  have  been  seen  passing  from  pons  to  tegmentum  and  also  imbedded 
in  the  medial  lemniscus  in  lower  levels  (pp.  449,  439).  Some  of  these  fibres  are 
possibly  fibres  acting  directly  or  indirectly  on  the  efferent  peripheral  neurones  or 
motor  nuclei  of  the  cranial  nerves. 

The  pallio-pontile  fibres  are  still  more  numerous.  The  gray  matter  in  the  pons 
(nuclei  pontis)  is  very  extensive.  The  transverse  fibres  of  the  pons  no  longer  pass 
at  this  level  into  the  cerebellum,  but  are  collected  at  the  sides  of  the  pons  to  pass 
backward  to  the  cerebellum  (compare  with  an  external  view  of  the  brain). 

The  superior  cerebellar  peduncles  or  brachia  conjunctiva  are  two  large  crescentic 
bundles  of  fibres  in  the  lateral  part  of  the  reticular  formation.  Some  of  their  fibres 
have  begun  to  decussate  in  the  ventral  part  of  the  reticular  formation. 

The  tecto-spinal  tract  or  predorsal  fasciculus  lies  ventral  to  the  medial  longitudi- 
nal fasciculus. 


Midbrain  or  Mesencephalon. 

The  dorsal  surface  of  the  midbrain  presents  four  rounded  promi- 
nences, the  two  posterior  and  the  two  anterior  corpora  cjuadrigemina 
or  the  inferior  and  superior  colliculi.  Ventrally  are  seen  two  di\erging 
masses  of  longitudinal  fibres,  the  pes  peduncuH,  separated  by  a  deep 
groove  or  sulcus.  In  the  midbrain  are  to  be  distinguished,  [a)  the 
expanded  roof,  the  corpora  quadrigemina,  (b)  the  tegmentum  containing 
the  segmental  (cranial  nerves  IV  and  III)  and  interscgm.ental  appa- 
ratus and  the  afferent  suprasegmental  paths,  and  (c)  the  basis  peduncuH, 
ventral  to  the  tegmentum  and  comi)rising  the  ])rincipal  efferent  pallial 
paths  {pes  pediincuti)  and  the  substantia  nigra. 

The  cavity  of  the  midbrain  is  the  aqueducliis  Sylvii  or  iter. 


THE  NERVOUS  SYSTEM.  4(io 

PRACTICAL  STUDY. 

lo.  Transverse  Section  through  Midbrain  at  Level  of  Anterior  Corpora 

Quadrigemina  and  Exit  of  Nerve  III  (Oculomotor).      (Figs.  295  and  317). 

Compared  with  the  preceding  section,  the  following  are  the  most  conspicuous 
changes:  The  roof  has  now  enlarged  into  the  anterior  corpora  quadrigemina  (or 
superior  colliculi);  the  tegmentum  now  contains  the  nuclei  and  roots  of  nerve  III 
and  the  red  nucleus;  instead  of  the  pons,  the  ventral  part  of  the  brain  is  now 
composed  of  the  basis  pedunculi,  consisting  of  a  mass  of  efferent  pallial  fibres  and 
the  substantia  nigra.  The  term  crura  cerebri  or  cerebral  peduncles  is  loosely  used 
to  include  all  except  the  roof  of  the  brain  at  this  level. 

Efferent  Peripheral  Neurones. — The  nucleus  of  nerve  III  or  oculomotor  nucleus 
is  located  in  the  ventral  part  of  the  central  gray  in  a  V-shaped  trough  formed  by  the 
fibres  of  the  medial  longitudinal  fasciculus.  The  nucleus  is  divided  into  large  and 
small-celled  groups.  The  large-celled  groups  are  two  lateral  groups  subdivded 
into  anterior  and  posterior  dorso-lateral  and  anterior  and  posterior  ventro-mesial, 
and  a  central  or  median  group — nine  in  all.  Between  the  cephalic  or  anterior 
groups  are  on  each  side  a  srhall-celled  group  known  as  the  Edinger-Westphal 
nucleus,  and  still  further  forward  are  two  small-celled  anterior  median  nuclei.  The 
connections  of  these  groups  with  the  extrinsic  muscles  of  the  eye  innervated  by 
nerve  III  (internal,  superior  and  inferior  recti,  and  inferior  oblique)  and  the  levator 
palpebrs  superioris  and  intrinsic  eye  muscles  (ciliary  and  sphincter  pupillcC,  via 
ciliary  sympathetic  ganglion)  are  uncertain.  From  a  priori  grounds,  the  innerva- 
tion of  the  intrinsic  muscles  by  the  small-celled  groups  and  the  other  muscles  by  the 
large-celled  groups  would  seem  probable.  Some  of  the  fibres,  usually  stated  to  be 
from  the  posterior  dorso-lateral  group,  decussate.  Recent  observations  (Cajal) 
would  indicate  that  the  decussating  fibres  come  from  the  ventro-mesial  lateral 
groups.  The  various  fibres  pass  ventrally  in  a  number  of  bundles,  some  passing 
mesial  to,  some  traversing,  and  some  passing  lateral  to  the  superior  cerebellar 
peduncle  and  red  nucleus.  Ventral  to  these  the  root  fibres  come  together  and 
emerge  on  the  ventral  aspect  of  the  midbrain.     (Figs.  317  and  318.) 

Immediately  caudal  to  the  nucleus  of  nerve  III  (not  in  the  plane  of  the  section) 
is  the  nucleus  of  the  nerve  IV  occupying  a  position  similar  to  the  lateral  groups 
of  the  nerve  III  nucleus.  The  course  of  the  root  fibres  of  the  IV  has  been  ment- 
tioned  (preceding  section). 

Afferent  Roots,  their  Terminal  Nuclei  and  Secondary  Tracts. — The 
mesencephalic  trigeminal  root  is  sometimes  distinguishable  on  the  lateral  border 
of  the  central  gray. 

The  lateral  lemniscus  has  partly  or  wholly  terminated  in  the  posterior  corpus 
quadrigeminum  (inferior  colliculus)  at  a  lower  level.  Fibres  from  the  latter  form 
its  arm  or  brachium,  representing  another  link  of  the  cochlear  path.  In  the  present 
section  the  fibres  of  the  brachium  of  the  posterior  corpus  quadrigeminum  are  jctn 
entering  the  medial  geniculate  body  (which  is  a  part  of  the  thalamus).  Axones  of 
the  cells  of  this  body  constitute  the  last  relay  of  the  cochlear  path  to  the  temporal 
cortex  cerebri  (not  present  in  this  section). 

The  medial  lemniscus  is  now  a  laterally  placed,  curved  bundle,  displaced  later- 
ally by  the  red  nucleus.  According  to  some  authorities,  some  of  its  fibres  terminate 
in  the  anterior  corpus  quadrigeminum.     The  spino-thalamic  tract  is  plainly  distin- 


466 


THE  ORGANS. 


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h-1  h 


THE  NERVOUS  SYSTEM.  40/ 

guishable  as  a  bundle  dorsal  to  the  dorsal  edge  of  the  medial  lemniscus.  At  this 
level,  then,  the  afferent  paths  from  cord  to  pallium  have  practically  united. 

In  the  anterior  corpus  quadrigeminum  are  terminations  of  the  optic  tract 
(so-called  optic  nerve)  (see  below). 

The  central  tegmental  tract  is  displaced  dorsally  by  the  red  nucleus. 

Intersegmental  Neurones. — The  reticular  formation  is  smaller.  The  rubro- 
spinal tract  (not  distinguishable)  is  emerging  from  its  nucleus  of  origin,  the  nucleus 
ruber.  Just  below  this  level  its  fibres  decussate  {ventral  decussation  of  Forel)  and 
pass  to  the  location  they  have  been  seen  to  occupy  in  preceding  levels.  The  nucleus 
ruber  or  red  nucleus  is  very  conspicuous,  occupying  a  large  part  of  the  reticular  for- 
mation.    It  gives  rise  to  rubro-bulbar  as  well  as  rubro-spinal  fibres. 

The  medial  longitudinal  fasciculus  is  diminished,  some  of  its  descending  fibres 
having  been  formed  from  reticular  formation  nuclei  below  this  level.  Many  of  its 
fibres,  both  ascending  and  descending,  send  collaterals  and  terminals  to  the  cells  of 
the  oculomotor  nucleus. 

Efferent  Suprasegmental  Neurones. — The  ventral  part  of  the  brain  is  com- 
posed of  a  mass  of  efferent  pallial  fibres,  the  pes  peduncidi.  The  pyramidal  fibres 
from  the  precentral  areas  of  the  cerebral  hemisphere  (pallio-spinal  and  some  pallio- 
bulbar  fibres)  occupy  about  the  middle  three-fifths,  but  are  also  scattered 
through  other  parts  of  the  pes,  especially  the  mesial  part.  The  leg  fibres  are 
probably  more  numerous  laterally,  the  arm  fibres  in  the  middle,  and  the  face  fibres 
mesially.  In  the  lateral  part  of  the  pes  are  pallio-pontile  fibres  from  the  occipital 
and  temporal  lobes  of  the  cerebral  hemispheres  (occipito-temporal  pallio-pontile 
fibres).  In  the  mesial  part  are  efferent  palHal  fibres  from  the  frontal  lobe,  in  part 
to  the  pons  nuclei  (frontal  pallio-pontile)  and  in  part  possibly  from  the  lower  frontal 
region  to  the  motor  nuclei  of  cranial  nerves  VH  and  XII.  There  is  also  the 
bundle  already  referred  to  (p.  464)  which  in  its  downward  course  passes  from  the 
lateral  part  of  the  pes  to  the  mesial  part  of  the  medial  lemniscus  and  is  variously 
stated  to  contain  fibres  from  cortex  cerebri  or  from  thalamus  to  the  medulla(p.  470). 

Dorsal  to  the  pes  and  constituting  the  remainder  of  the  basis  pedunculi  is  a 
mass  of  gray  matter  which,  on  account  of  the  pigmentation  of  its  cells,  is  known 
as  the  substantia  nigra.  This  receives  many  collaterals  and  terminals  of  efferent 
pallial  fibres  and  possibly  of  fillet  fibres.  The  destinations  of  the  axones  of  its  cells 
are  not  definitely  known.     They  are  stated  to  join  the  pes. 

The  superior  cerebellar  peduncle  has  completed  its  decussation  below  this  level 
and  its  fibres  are  seen  surrounding  or  within  the  nucleus  ruber  which  is  their  ter- 
minal nucleus,  as  well  as  the  nucleus  of  origin  of  the  rubro-spinal  tract. 

Internal  arcuate  fibres  from  the  gray  matter  of  the  anterior  corpus  quadrigemi- 
num pass  through  the  reticular  formation,  and  form  an  oblique  decussation.  This 
decussation  is  the  dorsal,  or  jountain-like  decussation  of  Meynerl.  The  fibres  origi- 
nate from  cells  in  the  anterior  corpus  quadrigeminum  (tectum  opticum),  and  after 
decussation  form  the  descending  tectospinal  (prcdorsal)  tract  or  ventral  langitudinal 
fasciculus  (see  also  below). 

The  Anterior  Corpus  Quadrigeminum  or  Superior  Colliculus. — In  this 
four  principal  lavers  mav  be  distinguished  besides  the  usual  covering  of  neuroglia 
cells  and  fibres:  (i)  An  outer  while  layer,  stratum  zoialc.  This  consists  of  fine 
nerve  fibres  coming  from  the  superior  brachium,  possibly  fibres   from   the  optic 


468  THE  ORGANS. 

tract  and  cerebral  cortex.  Among  them  are  small  nerve  cells,  mostly  horizontal 
and  with  tangential  or  centrally  directed  a.xones.  (2)  A  gray  layer,  the  stratum 
cinereitm.  This  consists  of  radially  arranged  nerve  cells  with  their  larger  dendrites 
proceeding  outward,  and  their  axones  inward.  The  largest  cells  lie  deepest.  In 
this  layer  the  optic  fibres  principally  terminate.  (3)  The  stratutn  opticuni  con- 
sists principally  of  optic  fibres  which  send  their  terminals  mostly  into  the  pre- 
ceding layer,  but  also  into  the  deeper  layers.  It  also  contains  cells  whose  axones 
pass  into  the  next  layer.  (4)  Deep  gray-white  layer,  or  stratum  leninisci,  because 
it  is  stated  to  contain  fibres  from  the  medial  lemniscus  which  terminate  in  the 
superior  colliculus  (denied  by  some).  This  layer  contains  large  and  medium 
stellate  cells  whose  axones,  together  with  axones  from  cells  in  the  more  super- 
ficial layers,  either  pass  across  to  the  opposite  colliculus  or  sweep  ventrally 
around  the  central  gray,  decussate  in  the  raphe  and  proceed  caudally  as  the 
tecto-spinal  tract.  The  above  relations  have  been  principally  ascertained  by  the 
Golgi  method.  The  superior  colliculus  also  possibly  receives  fibres  from  the 
lateral  lemniscus  and  spino-thalamic  tract.  It  also  receives  fibres  from  the  occipital 
and  temporal  cortex  cerebri. 

Belonging  to  the  midbrain  is  the  posterior  commissure  (not  in  the  section)  the 
fibres  of  which  cross  in  the  roof  just  anterior  to  the  superior  colliculus.  Its  fibres 
originate  from  collicular  cells  (in  turn  receiving  optic  fibres),  decussate  and  termi- 
nate in  the  interstitial  nucleus  and  other  nuclei  in  the  reticular  formation. 

The  colliculus  thus  consists  essentially  of  (a)  afferent  fibres  from  the  retina 
(optic  tract),  the  pallium  and  possibly  other  parts  of  the  nervous  system,  and  {b) 
efferent  neurones  to  other  parts  of  the  brain  and  cord  brought  into  various  relations 
with  each  other  in  the  colliculus  either  directly  or  by  (c)  the  association  cells  of 
the  colliculus,  the  axones  of  which  do  not  leave  the  latter. 

Forebrain  or  Prosencephalon, 

Interbrain  (diencephalon  or  thalamencephalon). 

In  the  interbrain  or  diencephalon,  three  parts  may  be  distinguished; 
the  thalamus,  epithalamus,  and  hypothalamus.  The  epithalamus  consists 
principally  of  the  pineal  body,  the  habenulse,  and  stride  thalami.  The 
hypothalamus  consists  mainly  of  the  structures  in  the  ventral  expansion 
of  the  interbrain,  such  as  the  corpora  mamillaria,  tuber  cinereum,,  in- 
fundibulum  and  jxjsterior  lobe  of  the  hypophysis.  The  epithalamus 
and  hypothalamus  are  principally  connected  with  olfactory  paths  (see 
p.  477  and  Fig.  321).  Certain  extensions  forward  of  the  tegmentum 
are  also  termed  subthalamic  (t^,^^,  corjjus  subthalamicum  or  cor])us 
Luysii). 

The  thalamus  comprises  the  great  bulk  of  the  interljrain.  It  con- 
sists of  a  number  of  nuclei  forming  links  in  afferent  and  efferent  jiallial 
paths  and  of  other  nuclei  connected  with  the  corpora  striata.  There 
is  much  difference  of  opinion  both  as  to  the  number  of  the  nuclei  and 


THE    NER\-()IS    SYSTEM.  409 

their  connections.  According  to  some  authorities  the  thalamus  may  be 
regarded  as  di\ided  into  internal  and  external  segments  (usually  sepa- 
rated by  the  lamina  medullaris  medialis).  The  internal  segm.ent  con- 
sists of  an  anterior  nucleus,  median  nucleus,  the  "median  center"  or 
nucleus  of  Luys,  and  a  nucleus  arcuatus.  The  external  segment  con- 
sists of  a  dorso-lateral,  an  external  ventro-lateral,  an  internal  ventro- 
lateral, and  a  ventral  nucleus.  To  the  external  segment  should  be  added 
the  pulvinar  and  lateral  and  medial  geniculate  bodies  (metathala- 
mus).  The  various  nuclei  of  this  external  segment  receive  the  fibres  of 
the  afferent  pallial  paths  and  complete  the  paths  by  sending  fibres  to 
the  cortex  pallii.  These  paths  are  (i)  the  medial  lemniscus,  spino- 
thalamic, and  secondary  trigeminal  tracts  (general  sensory  from  body 
and  face)  to  the  ventro-lateral  nuclei  and  thence  to  the  cortex  of  the 
central  region  of  the  pallium;  (2)  the  lateral  fillet  or  brachium  of  inferior 
colliculus  (hearing)  to  the  medial  geniculate  body,  and  thence  to  the 
temporal  region  of  the  pallium;  (3)  the  optic  tract  to  the  lateral  genicu- 
late body  and  thence  to  the  occipital  pallial  cortex;  (4)  part  of  the  supe- 
rior cerebellar  peduncle  (also  said  to  be  distributed  to  nuclei  of  inner 
segment).  The  visceral  (including  gustatory)  and  vestibular  paths  to 
the  pallium  are  not  definitely  known.  As  the  olfactory,  nerve  belongs 
to  the  endbrain,  its  path  to  the  pallium  does  not  traverse  the  thalamus. 
Besides  giving  rise  to  the  above  thalamo-cortical  fibres,  the  external 
thalamic  segment  in  all  probability  receives  many  descending  fibres 
from  the  cortex  pallii.  The  various  fibres  connecting  thalamus  and 
cortex  constitute  the  thalamic  radiations.  In  general  the  anterior  parts 
of  the  cortex  are  connected  with  the  anterior  part  of  the  external 
thalamic  segment,  the  middle  with  the  middle,  and  the  posterior  with 
the  posterior.  It  is  also  probable  that  the  thalamo-cortical  fibres 
from  the  various  lateral  nuclei  are  arranged  dorso-ventrally,  so  that  the 
fibres  from  the  ventral  parts  pass  to  the  ventral  part  of  the  central 
region  of  the  pallium,  dorsal  to  dorsal,  etc.     (E.  Sachs.) 

The  nuclei  of  the  internal  segment  of  the  thalamus  do  not  appear, 
according  to  some  recent  researches,  to  have  direct  connections  with 
the  cortex  pallii.  The  anterior  nucleus  receives  the  bundle  of  \'icq  d' 
Azyr  (mamillo-thalamic  tract)  and  probably  sends  fibres  to  the  nucleus 
caudatus  (see  p.  478).  It  thus  belongs  to  the  olfactory  apparatus. 
The  median  nucleus  is  also  probably  connected  with  the  nucleus  cau- 
datus. The  median  center  of  Luys  and  the  nucleus  arcuatus  send 
fibres  to  adjoining  thalamic  nuclei,  especially  the  lateral  nuclei,  and 
appear  to  be  thus  association  nuclei.      Other  authorities  afiirm  that 


470  THE  ORGANS. 

ascending  tracts  are  received  by  some  of  these  internal  nuclei  and  that 
they  have  direct  cortical  connections. 

Descending  tracts  coming  directly  from  the  thalamus  have  not  been 
definitely  demonstrated.  The  ventral  nucleus  appears  to  send  fibres 
to  the  nuclei  of  the  cranial  nerves  V,  VI,  \TII,  and  X,  via  the  medial 
longitudinal  fasciculus.     (E.  Sachs.) 

PRACTICAL  STUDY. 

II.  Transverse  Section  through  the  Junction  of  Midbrain  and  Thalamus. 

(Figs.  295  and  318.) 

The  most  conspicuous  change  from  the  last  section  is  the  appearance,  or  in- 
crease, of  the  geniculate  bodies  and  pulvinar,  and  the  thalamic  radiations. 

Efferent  Peripheral  Neurones. — The  nuclei  and  root  fibres  of  the  III  nerve 
are  still  present. 

Afferent  Roots,  their  Terminal  Nuclei,  Secondary  Tracts,  and  Tertiary 
Neurones. — The  fibres  of  the  optic  tract  (optic  "nerve")  are  seen  entering  the 
ventral  surface  of  one  of  their  terminal  nuclei,  the  lateral  or  external  geniculate  body. 
Other  optic  fibres  (not  entirely  traceable)  enter  the  pulvinar  thalami  and  the 
superior  colHculus  {Stro)  (see  also  preceding  section).  On  the  dorso-lateral  surface 
of  the  lateral  geniculate  body,  a  bundle  of  fibres  accumulates  which  represents 
the  beginning  of  the  geniculo-calcarine  tract  to  the  occipital  cortex,  thereby  com- 
pleting the  visual  path. 

Internal  to  the  lateral  geniculate  body  is  the  medial  (internal)  geniculate  body 
which  now  contains  the  terminals  of  the  brachium  of  the  inferior  colliculus.  Fibres 
from  its  cells  gather  on  its  lateral  surface.  These  represent  the  beginning  of  the 
geniculo-temporal  tract  to  the  temporal  cortex,  thereby  completing  the  auditory 
path. 

Internal  and  ventral  to  the  medial  geniculate  body  are  the  medial  lemniscus 
(bulbo-thalamic)  and  spino-thalamic  tracts  about  to  terminate  in  the  ventro-lateral 
thalamic  nuclei  whose  axones  complete  the  general  sensory  path  by  passing  to  the 
central  cortex. 

The  central  tegmental  tract  can  hardly  be  distinguished. 

Intersegmental  Neurones. — The  nucleus  ruber  is  still  large,  but  the  remainder 
of  the  reticular  formation  has  nearly  disappeared.  The  medial  longitudinal  fascic- 
ulus is  much  diminished  as  its  ascending  fibres  terminate  in  the  nucleus  of  nerve 
III  and  many  of  its  descending  fibres  originate  from  cells  below  this  level. 

Efferent  Suprasegmental  Neurones. — The  pes  pedunculi  occupies  the  same 
position,  and  dorsal  to  it  is  the  diminished  substantia  nigra.  Along  the  ventro- 
mesial  border  of  the  pes  a  bundle  of  fibres  can  sometimes  be  distinguished  (Fig. 
318,  Lmp),  which  at  lower  levels  comes  to  lie  mesial  to  the  medial  lemniscus 
(ah)errant  peduncular  fibres,  comp.  p.  467).  Descending  pallial  fibres  (not  dis- 
tinguishable) also  probably  form  part  of  the  thalamic  radiations  (pp.  469,  472). 

Fibres  of  the  superior  cerebellar  peduncle  may  be  seen  within  and  around 
the  nucleus  ruber.  Some  of  these  terminate  in  the  latter,  some  pass  further  for- 
ward to  end  in  the  thalamus  (compare  pp.  455,  469). 


THE  NERVOUS  SYSTEM. 


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472  THE  ORGANS. 

The  Anterior  Corpus  Quadrigeminum  is  somewhat  diminished.  The 
posterior  commissure  passes  across  in  the  roof  dorsal  to  the  central  gray  (see 
preceding  section). 

The  Thalamus  (can  hardly  be  included  under  the  preceding  structures). — 
The  corpora  geniculata  have  been  mentioned.  The  pulvinar  thalami  is  a  large 
gray  mass  dorsal  to  the  medial  geniculate  body.  Fibres  passing  laterally  from  it 
contribute  to  the  retr denticular  portion  of  the  internal  capsule  (Cirl).  These  fibres 
are  a  part  of  the  thalamic  radiations. 

The  nucleus  caudatus  (a  portion  of  the  corpus  striatum  of  the  endbrain)  is 
present. 

12.  Section  through  the  Interbrain  at  the  Level  of  the  Optic  Chiasma. 
(Figs.  295  and  319.) 

Efferent  Peripheral  Neurones. — None  present. 

Afferent  Roots,  their  Terminal  Nuclei,  Secondary  Tracts,  and  Tertiary 
Neurones. — Fibres  of  the  optic  nerve  are  seen  decussating  and  forming  the  optic 
chiasma.  The  further  continuation  of  the  optic  fibres  to  their  termination  is  called 
the  optic  tract.  Both  nerve  and  tract  constitute  the  secondary  optic  tract,  the  optic 
chiasma  being  analogous  to  the  decussation  of  the  medial  lemniscus  and  of  the 
lateral  lemniscus  (trapezius).     (For  further  description  of  optic  paths  see  Fig.  320.) 

The  medial  lemniscus,  spino-thalamic,  and  secondary  trigeminal  tracts  are  now 
lost  in  the  ventro-lateral  thalamic  nuclei,  cells  of  which  constitute  the  tertiary 
neurones  of  the  various  afferent  pallial  paths  (see  pp.  469  and  470). 

Intersegmental  Neurones. — The  cephalic  end  of  the  nucleus  ruber  is  still 
present  on  the  right  (Ntg).  On  the  left  are  seen  some  fibres  in  its  place,  lateral 
to  which  are  two  transverse  bundles  enclosing  a  strip  of  gray  matter.  These  are 
known  as  the  area  tegmenti  or  field  of  Forel  and  represent  a  subthalamic  forward  ex- 
tension of  the  tegmentum.  The  gray  or  zona  incerta  may  be  regarded  as  represent- 
ing a  continuation  of  part  of  the  reticular  formation.  The  ventral  bundle  of  fibres 
{HII)  are  probably  fibres  from  the  red  nucleus  passing  through  the  pes  as 
perforating  fibres  {fp  on  right)  to  the  globus  pallidus  {glp,  right).  The  dorsal 
bundle  (HI)  probably  represents  fibres  connecting  red  nucleus  and  pallium,  proba- 
bly from  pallium  to  red  nucleus.  Other  fibres  in  this  region  are  probably  fibres 
of  the  superior  cerebellar  peduncle  which  have  passed  by  the  nucleus  ruber  to  the 


Fig.  319. — Section  thnjugh  the  Interbrain  at  the  Level  of  the  Optic  Chiasma.  (The 
chorioid  plexus  of  the  third  ventricle  has  been  removed.)  Weigert  preparation.  (Mar- 
burg.) Ce,  Capsula  externa;  Cex,  capsula  extrema;  Chll,  chiasma  nervorum  opticorum 
(or  optic  chiasma);  Ci,  capsula  interna;  CI,  claustrum;  Cml,  ganglion  laterale  corp. 
mammillaris;  Cmm,  ganglion  mediale  corp.  mammill.;  Coa,  commissura  anterior;  Cospm, 
commissura  supramammillaris;  C.s-</t,  corpus  subthalamicum;^,  nucleus  externus  ganel. 
meri.  corpor.  mammillaris;  Fmp,  fasciculus  mammillaris  jjrinceps;  Fo,  fornix;  Fp,  fibrtc 
jjerforantes  (perlunculi); /r//,  fasciculus  retroOexus  (Meynert) ;  /^.y/^,  fasciculus  subthal- 
amico-pcduncularis;  Fu,  fasciculus  uncinatus;  (!hb,  ganglion  habenuhe;  i!;lp,  globus  jjalli- 
flus;  Jf,  area  tegmenti  Forel;  ///,  pars  dorsalis  areiu  tegmenti;  HII,  pars  ventralis  area- 
tegmenti;  /,  insula  Reillii;  i,  nucleus  internus  gangl.  mdial.  corp.  mammillaris;  Lml, 
lamina  medullaris  lateralis;  Narc,  nucleus  arcuatus  thalami;  No,  nucleus  caudatus; 
NL,  nucleus  Luysii  (nucleus  centralis,  or  median  centre,  thalami;  Nl,  nucleus  lateralis 
thalami;  Nlv,  nucleus  lateralis  ventralis  thalami;  Ntg,  nucleus  ruber  tegmenti;  Pp, 
pes  pedunculi;  Pu,  putamcn;  .S'^^.S',  substantia  nigra;  St,  stria  cornea;  Strz,  stratum  zonale 
thalami;  Til,  tractus  opticus;  The,  tuber  cinereum;  Tt,  taenia  thalami;  VIII,  ven- 
triculus  tertius;  Zi,  zona  incerta. 


THE  NERVOUS   SYSTEM. 


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474 


THE  ORGANS. 


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THE   NERVOUS   SYSTEM.  475 


EXPLANATION  OF  FIG.  320. 

Fig.  320. — Diagram  of  the  Optic  (II)  Nerve  and  some  of  its  Principal  Connections. 
A,  Level  of  nerves  II  and  III;  B,  level  of  nerve  IV;  C,  level  of  nerves  VI  and  VII;  D, 
spinal  cord.     Neurone  groups  are  represented  by  one  or  several  individual  neurones. 

The  rods  and  cones  (receptors)  and  the  bipolar  cells  (  =  Neurone  No.  i)  of  the 
retina  are  not  indicated. 

Neurone  N^o.  2. — 2  a,  Axones  of  ganglion  cells  in  temporal  part  of  retina  pass  to  pulvinar 
of  thalamus  of  same  side;  2  b,  axones  of  ganglion  cells  in  temporal  retina  pass  to  anterior 
corpus  quadrigeminum  of  same  side;  2  c,  axones  of  ganglion  cells  in  temporal  retina  pass 
to  external  geniculate  body  of  same  side;  2  e,  axones  of  ganglion  cells  in  nasal  side  of 
retina  cross  in  optic  chiasma  and  pass  to  external  geniculate  body  of  opposite  side;  2/. 
axones  of  ganglion  cells  in  nasal  side  of  retina  cross  in  optic  chiasma  and  pass  to  anterior 
corpus  quadrigeminum  of  opposite  side;  2  g,  axones  of  ganglion  cells  in  nasal  side  of  retina 
cross  in  optic  chiasma  and  pass  to  pulvinar  of  thalamus  of  opposite  side.  Macular  fibres 
are  partly  crossed  and  partly  uncrossed. 

Neurone  No.  3. — 3  a,  Axones  of  cells  in  pulvinar  to  cortex  of  occipital  lobe  of  cerebrum 
(this  connection  is  disputed);  3  b,  axones  of  cells  in  external  geniculate  body  to  cortex  of 
occipital  lobe  of  cerebrum;  3  a  and  3^  constitute  the  primar}^  optic  radiation;  t,  c,  t,  d  and 
3  e,  axones  of  cells  in  middle  layer  of  tectum  (roof)  of  anterior  corpus  quadrigeminum 
decussate  ventral  to  medial  longitudinal  fasciculus  (dorsal  tegmental  decussation  or 
decussation  of  ]Meynert)  and  form  the  tractus  tecto-bulbaris  et  spinalis  or  predorsal  bundle. 
(Tr.  tectobulb.  et  spin.)  to  bulb  (medulla)  and  anterior  column  of  cord,  innervating  by 
collaterals  and  terminals,  directly  or  indirectly,  chiefly  the  nuclei  of  III,  IV,  \I,  and  ^TI 
cranial  nerves  and  motor  nuclei  of  spinal  nerves.  3  /  and  3  g  (possibly  another  neurone 
intercalated  between  these  and  optic  terminals),  axones  of  cells  in  interstitial  nucleus  of 
Cajal  (Nu.  fasc.  long,  post.)  form  part  of  medial  longitudinal  fasciculus  and  descend  on 
same  side  to  anterior  column  of  cord  next  to  anterior  median  fissure,  innervating  nuclei  of 
III,  IV,  and  VI  cranial  nerves  and  motor  nuclei  of  spinal  nerves. 

Neurone  No.  4. — •x\xones  of  cells  in  above-mentioned  motor  nuclei.  Axones  from  cells 
in  median  nucleus  of  nerve  III  (Nu.  med.  Ill  N.)  and  possibly  in  Edinger-Westphal  nu- 
cleus, probably  innervate  the  intrinsic  muscle  of  eveball  (ciliary  and  pupillary  reflex  path). 

Pallio-tectal  fibres,  by  means  of  which  the  quadrigeminal  reflex  centre  is  brought 
under  the  control  of  the  cerebral  cortex,  are  not  indicated. 

It  is  evident  from  the  diagram  that  the  cerebral  pathway  of  the  optic  nerve  is  via  the 
external  geniculate  body  (and  pulvinar  of  thalamus  ?),  and  the  reflex  pathway  is  via  the 
superior  colliculus  (anterior  corpus  quadrigeminum). 


476 


THE  ORGANS. 


lateral  nucleus  and  median  center  of  the  thalamus  (see  also  p.  469).     The  intersti 
tial  nucleus  of  Cajal  falls  in  the  level  between  this  and  the  preceding  section. 

Efferent  Suprasegmental  Neurones. — The  pes  pedunculi  now  lies  partly 
between  the  thalamus  and  nucleus  lenticularis  (see  p.  478)  constituting  the  greater 
part  of  the  internal  capsule.  The  parts  of  the  internal  capsule  as  shown  in  horizon- 
tal sections  of  the  hemispheres  are  shown  in  figure  322.  The  most  dorsal  part  is 
here  passing  into  the  corona  radiata  (p.  478)  of  the  cerebral  hemispheres  (not 
included  in  the  section).  The  part  present  in  this  level  is  the  most  posterior  part 
of  the  capsule  (occipito-temporal  pallio-pontile  fibres  (see  p.  479). 


Fig.  .321. — Diagram  of  Olfactory  Paths  (von  Bcchterew.)  A',  Root  fibres  of  vagus; 
ca,  commisura  anterior;  cm,  corpus  mammillare;  cp,  fibres  from  nucleus  habenuke  to 
posterior  commissure; /G,  tract  from  corpus  mammillare  to  Oudden's  nucleus;  fi,  fasciculus 
mammillo-thalamicus;/,  fasciculus  longiludinalis  medialis;  fr,  fornix;  fid,  fibres  of  fornix 
longus;  gh,  nucleus  habenulse;  gi,  ganglion  inlerpedunculare;  gp,  gyrus  pyriformis;  /, 
lemniscus  medialis;  m,  fibres  from  Oudden's  nucleus  to  substantia  reticularis  grisea;  na, 
nucleus  anterior  thalami;  nG,  Oudden's  nucleus;  nt,  nucleus  tegmenti  (v.  Oudden);  nX, 
nucleus  molorius  nervi  vagi;  pcE,  pedunculus corporis  mammillaris  from  fillet;  qa,  corpora 
quadrigemina;  r,  fibres  from  nucleus  tegmenti  (v.  Oudden)  to  nuclei  of  cranial  nerves;  re, 
radix  lateralis  tractus  olfactorii;  rf,  fibres  of  tractus  olfaclorius  to  trigonum  olfactorium; 
ro,  radix  medialis  tractus  olfactorii;  s,  fibres  from  ganglion  inlerpedunculare  to  nucleus 
tegmenti;  so,  area  of  trigonum  olfactorium;  Ih,  thalamus;  Iro,  tractus  olfactorius;  It, 
tienia  thalami;  :x:,  fasciculus  retroflexus. 


THE   NERVOUS   SYSTEM.  477 

Dorsal  to  the  mesial  part  of  the  pes  is  the  corpus  sublhalamicum  which  has 
replaced  the  substantia  nigra.  It  receives  collaterals  from  the  pes  and  is  said  to 
contribute  fibres  to  the  latter.  Superior  cerebellar  peduncle  (see  Intersegmental 
Neurones  above). 

Thalamus. — At  this  level  the  vcnlro-lateral  )iitcleiis,  the  nucleus  arcuatus,  and 
the  median  center  oj  Luys  can  usually  be  distinguished.  At  the  outer  border  of  the 
thalamus,  fibres  accumulate  forming  the  lateral  medullary  lamina.  These  fibres 
continue  outward  as  thalamic  radiations,  entering  the  internal  capsule  which  they 
may  follow  a  distance,  or  cross  obliquely  and  enter  the  corona  radiata. 

Epithalamic  and  Hypothalamic  Structures  and  their  Connections. — 
The  ganglia  habenulce  are  two  small  masses  of  gray  matter  occupying  eminences  on 
the  mesial  walls  of  the  thalamus.  A  bundle  of  fibres  near  each  is  the  stria  medul- 
laris  (near  the  tcenia  thalami)  consisting  of  fibres  from  the  olfactory  bulb  and 
trigonum  and  representing  afferent  olfactory  connections  (p.  478).  The  ganglion 
habenulae  contains  a  mesial  small-celled  and  a  lateral  large-celled  nucleus.  Their 
axones  form  the  fasciculus  retroflexus  of  Meynert  to  the  interpeduncular  ganglion, 
situated  more  caudally  (Fig.  321).  There  is  also  a  commissura  habenularis  connect- 
ing the  two  ganglia.  The  stria  terminalis  {stria  cornea),  another  olfactory  connec- 
tion, lies  in  the  groove  between  the  ventricular  surfaces  of  nucleus  caudatus  and 
thalamus.  The  tuber  cinereum  is  seen  projecting  ventrally.  Dorsal  to  this  are 
seen  the  corpora  mammiUaria  containing  lateral  and  mesial  nuclei.  The  mammillary 
body  receives  the  fibres  of  the  jornix  (from  the  rhinopallial  cortex,  see  below) 
and  also  fibres  from  the  medial  fillet.  It  gives  rise  to  the  bundle  of  Vicq  d'Azyr 
(mammillo-thalamic  tract)  to  the  thalamus,  and  mammillo-tegmental  fibres  to  the 
nucleus  of  Gudden  (Fig.  321)  and  red  nucleus.  The  fibres  entering  the  mammillary 
body  from  the  fillet  (and  other  sources)  constitute  its  peduncle.    ( See  also  Endbrain) . 

On  the  right  is  seen  the  posterior  part  of  the  nucleus  lenticularis  of  the  corpus 
striatum. 

The  Endbil4in  or  Telencephalon. 

The  endbrain  consists  of  pallium  (dorsal  expanded  part),  corpus 
striatum,  and  rhinencephalon.  Two  principal  parts  of  the  j^allium  may 
be  distinguished;  the  olfactory  pallium  or  rhinopallium  (archipallium) , 
including  principally  the  cornu  ammonis  and  gyrus  dentatus;  and  the 
neopallium  including  the  greater  part  of  the  cerebral  hemispheres. 
The  rhinencephalon^  includes  the  olfactory  nerves  and  bulb,  the 
trigonum  olfactorium,  the  tuberculum  olfactorium  or  anterior  per- 
forated space,  and  the  gyrus  hippocampi,  in  part  at  least  (pyriform 
lobe). 

The  olfactory  nerve  is  composed  of  axones  of  cells  in  the  olfactory 
mucous  membrane  which  terminate  in  the  olfactory  bulb.  They 
there  form  synapses  with  the  dendrites  of  the  mitral  cells,  the  axones 
of  which  constitute  the  secondary  tract,  part  of  which  decussates  in  the 

'  The  term  rhinencephalon  is  often  used  to  include  also  the  olfactory  pallium. 


478 


THE  ORGANS. 


pars  olfactoria  of  the  anterior  cerebral  commissure.  A  secondary 
tract  ("lateral  root")  proceeds,  with  tertiary  tracts,  to  the  cortex  of  the 
gyrus  hippocampi  and  thence  to  the  cornu  ammonis.  Efferent  axones 
of  cornu  ammonis  cells  are  collected  in  the  fimbria  and  descend  by  the 
fornix  to  the  mammillary  body,  the  further 
caudal  connections  of  which  have  been  de- 
scribed (p.  477).  Fibres  of  the  fimbria  also 
cross,  forming  the  commissure  of  the  fornix 
(olfactory  pallial  commissure).  Secondary 
olfactory  tracts  also  pass  to  the  trigonum, 
whence  tertiary  neurones  pass  as  the  stria 
medullaris  to  the  ganglion  habenulse  (see  p. 
477  and  Fig.  321).  The  principal  com.missure 
of  the  rhinencephalon  is  the  anterior  cerebral 
commissure. 

The  corpus  striatum  consists  of  the  nucleus 
caudatiis    and  nucleus    lenticularis,    the    con- 
nections  and   significance    of   which  are  ob- 
FiG.  322.— Scheme  of  Gen-    scurc.      They  receive  collaterals  from  the  de- 
irintemafcTpsuie^  ^vo'r    scending  pallial  fibres  which  pass   by  them 
Bechterew.)     I,  II,  III,    and  also  apparently  send  out  fibres  to  join 

The     three    parts   of    the 

lenticular  nucleus;  tic,  nu-    the  latter.      They  also  have  connections  with 


cleus  caudatus;  Fh,  thala- 
mus; gp,  globus  pallidus; 
pt,    putamen;    i,  fibres  of 


rhinenencephalon  and  thalamus. 

The    pallium    consists  of    an   extensive   ex- 
anterior  thalamic  peduncle;     ,  1  1     ,      1      1        .        r  j^j.        /         1 

2,  fibres  of  medialffrontal)  ternal  convoluted  sheet  of  gray  m^atter  {cortex 
pons  system;  ,3,  fibres  of    w//f  or  coi'tex  cerebri)   and  of  white  matter 

motor   cranial    nerves;    4, 

pyramidal  fibres;  5,  pyra-  underlying  the  gray.  In  the  white  m.atter 
rhLt',f[SaSMt*  -"ay  be  distinguished  the  corona  radiala 
sory)  path;  6,  fibres  of  the    composcd  of  the  afferent  and  efferent  pallial 

lateral  pons  system.     The      _,  .  ,  ...  •  1         1 

various  systems  are  not  fibres  connecting  the  pallium  With  Other  parts 
sharply  marked  off  as  in-    qJ  ^j^g  j^j-^j^  (projection  fibres).     The  remain- 

dicated,   but  are  more  or  /       j  ./  / 

less  intermingled.  ing  fibres  of  the  white  matter  are  association 

fibres  of  the  pallium  and  are  either  crossed 

or  com.missural,  connecting  the  two  hemispheres  {corpus  callosum  and 

fornix  commissure),  or  arc  uncrossed.     The  term  association  fibres  is 

often  restricted  to  the  latter. 

The  afferent  connections  of  the  neoj^allium  (p.  469)  and  rhino- 
palh'um  fpfj.  477,  478)  have  been  summarized  and  also  the  efferent 
connections  of  the  rhinopallium  (p.  478). 

The  following  are  the  princijjal  descending  or  efferent  connections 


THE  NERVOUS   SYSTEM.  479 

of  the  neopallium:  (i)  The  pyram.idal  or  pallio-spinal  tract.  This  is 
composed  of  the  axones  of  the  giant  cells  (of  Betz)  of  the  arm,  body,  and 
leg  precentral  motor  areas.  They  descend  in  the  corona  radiata,  the 
posterior  limb  of  the  internal  capsule,  middle  part  of  the  pes,  and 
thence  through  pons  and  medulla  to  the  cord.  Their  decussation  and 
further  course  has  been  described.  (2)  The  descending  tracts  to  the 
motor  nuclei  of  the  cranial  nerves  originate  from  precentral  cells  of 
the  various  areas  controlling  the  muscles  in  question  and  pass  down 
in  the  vicinity  of  the  genu  of  the  internal  capsule.  Their  path  is 
not  so  well  known  but  they  apparently  do  not  pass  down  in  the  pes 
throughout  their  course  (pp.  470,  467,  etc.).  (3)  The  pallio-pontile 
system  to  the  pons  (continuation  to  opposite  cerebellar  hemisphere). 
This  originates  in  various  parts  of  the  cortex.  The  fibres  from  the 
occipital  and  temporal  regions  pass  down  in  the  extreme  posterior 
part  of  the  internal  capsule  and  lateral  part  of  the  pes,  those  from  the 
frontal  region  pass  down  in  the  anterior  limb  of  the  internal  capsule 
and  mesial  part  of  the  pes.  (4)  Pallio-tectal  fibres  to  the  midbrain 
roof.  (5)  Fibres  to  the  substantia  nigra  and  corpus  subthalamicum. 
(6)  Fibres  to  the  red  nucleus.  (7)  Pallio-thalamic  fibres  (see  p.  469). 
(8)  Fibres,  or  collaterals,  to  the  corpora  striata.      (Fig.  322.) 

The  crossed  association  fibres  of  tJie  neopallium  (corpus  callosum) 
connect  principally  corresponding  parts  of  the  hemispheres.  The 
long  uncrossed  association  fibres  (furthest  from  the  gray  matter) 
form  certain  more  or  less  well-defined  bundles  among  which  are  the 
following:  (i)  The  cingulum,  a  longitudinal  bundle  near  the  corpus 
callosum;  also  contains  projection  fibres  and  belongs  to  the  olfactory 
part  of  the  brain  as  well  as  to  the  neopallium,.  (2)  The  superior 
longitudinal  fasciculus  or  fasciculus  arcuatus;  connects  frontal  with 
occipital  and  part  of  temporal  lobes.  (3)  The  inferior  longitudinal 
bundle  connecting  temporal  and  occipital  lobes.  It  may,  however, 
be  a  projection  bundle.  (4)  The  uncinate  fasciculus  connecting  frontal 
and  temporal  lobes.  (5)  The  perpendicular  fasciculus  of  Wernicke 
connecting  inferior  parietal  and  fusiform  lobules.  Projection  fibres 
may  form  portions  of  these  bundles. 

Shorter  association  fibres  nearer  the  gray  matter  connect  adjoining 
convolutions  (fibras  propriae  of  Meynert)  and  in  the  grav  matter  itself 
are  fibres  which  fall  under  this  category. 


480 


THE  ORGANS. 


PiTh 


Coa     X  Vli  ti  Roi)Fli 


Fig.  323. — Transverse  Section  through  the  Cerebral  Hemispheres,  Corpora  Striata 
and  Thalamus.  Weigert  preparation.  (Dejerine.)  //,  Tractus  opticus;  Alent,  ansa 
lenticularis;  c,  sulcus  centralis  (Rolandicus);  C'a,  gyrus  centralis  anterior;  Cell,  corpus 
callosum;  Ce,  capsula  externa;  CFo,  columna  fornicis;  Cia,  crus  anterior  capsul.  int.; 
Cig,  genu  capsul.  int.;  CI,  claustrum;  dim,  sulcus  callosomarginalis;  Cng,  cingulum; 
Coa,  commissura  anterior;  Cp,  gyrus  centralis  posterior  (ascending  parietal  convolution); 
CR,  corona  radiata;  Far,  fasciculus  arcuatus;  Fli,  fasciculus  longitudinalis  inferior; 
Frn,  gyrus  fornicatus;  fs,  .sulcus  frontalis  superior;  Fs,  gyrus  fnjntaiis  superior;  Fu, 
fasciculus  uncinatus;  Fus,  gyrus  fusiformis;  glp,  globus  pallidus  (inner  segment);  glp[, 
globus  pallidus  (outer  segment);  /,  insula;  Ime,  lamina  medullaris  externa  nuclei  lenti- 


THE  NERVOUS   SYSTEM.  481 


PRACTICAL  STUDY. 


13.  Transverse  Section  through  the  Cerebral  Hemispheres,  Corpora  Striata 
and  Thalamus.     (Fig.  7,2^  ) 

First  distinguish  in  general  (i)  the  pallium,  its  cortex  and  white  matter,  (2) 
the  corpus  striatum  and  its  divisions,  i.e.,  the  caudate  nucleus  and  the  putamen 
and  globus  pallidus  (two  subdivisions  of  the  lenticular  nucleus)  and  (3)  the  thala- 
mus and  other  structures  of  the  interbrain. 

Afferent  Roots,  their  Terminal  Nuclei,  Secondary  Tracts,  and  Tertiary 
Neurones. — The  optic  tract  here  forms  a  part  of  the  ventral  surface  of  the  brain. 
The  geniculo-cortical  portion  of  the  optic  path  forming  a  part  of  the  optic  radiation 
may  be  seen.  Other  afferent  pallial  connections  are  hardly  distinguishable  among 
the  fibres  connecting  thalamus  and  pallium. 

Efferent  Suprasegmental  Neurones. — A  great  part  of  the  pes  has  now  entered 
the  corona  radiata.  The  part  now  about  to  enter  the  corona  is  the  anterior  limb 
of  the  internal  capsule  (Fig.  322).  The  ansa  lenticularis  is,  according  to  some 
authorities,  composed  of  fibres  or  collaterals  from  the  pes  to  the  lenticular  nucleus. 
The  fibres  of  the  anterior  peduncle  of  the  thalamus  are  evident.  Thev  are  con- 
sidered by  some  as  composed  of  cortico-thalamic  fibres.  The  anterior  pillars  oj  the 
fornix  (efferent  rhinopallial)  are  shown  cut  through  twice,  the  upper  section  shows 
its  earlier  course  emerging  from  the  fimbria,  the  lower  section  is  near  its  termina- 
tion in  the  mammillary  body. 

For  other  structures  of  thalamus,  epithalamus,  and  hypothalamus  see  Fig.  323. 

The  Pallium. — In  the  white  matter  distinguish  as  far  as  possible  the  corona 
radiata,  the  corpus  callosum,  and  the  long  association  bundles  {inferior  longitudinal 
fasciculus,  fasciculus  uncinatus,  and  fasciculus  arcuatus)  (see  p.  479).  Note  the 
nucleus  amygdaliformis,  the  anterior  perforated  space  and  the  anterior  commissure, 
belonging  to  the  rhinencephalon. 

Other  details  shown  in  figure  323  should  be  studied. 

The  Cerebral  Cortex. — The  following  types  of  cells  are  found  in 
the  cerebral  cortex:  (i)  Pyramidal  cells.  This  is  the  prevailing  type 
and  is  characterized  by  a  long  apical  dendrite  usually  directed  toward 
the  surface  of  the  brain.  This  dendrite  gives  off  branches,  and  usually 
reaches  the  outer  cortical  layer,  there  to  break  up  into  a  number  of 
branches.     From  the  cell  body  are  also  given  off'  a  number  of  basal 

cularis;  Ime',  supplementary  lamina  of  the  outer  segment  of  the  globus  pallidus:  /;«/, 
lamina  medullaris  interna  nuclei  lenticularis;  nip  and  lus,  sulcus  circularis  (Reili):  XA, 
nucleus  amygdaliformis;  A"c,  nucleus  caudatus;  OpR,  operculum;  oli,  sulcus occipitotem- 
poralis  inferior;  pCR,  pes  coronae  radiate;  PiTh,  pedunculus  inferior  thalami;  prs, 
sulcus  pra;centralis;  Pu,  putamen;  rcc,  stratum  reticulum  corona;  radiata^;  Rop.  radiatio 
optica;  5,  fissura  Sylvii  (posterior  branch);  Sgc,  substantia  grisea  centralis;  sM,  sulcus 
Monroi;  ^o-f,  substantia  grisea  subependymalis;  ssc,  stratum  subcallosum;  ^/r",  stratum 
zonale  thalami;  Tbc,  tuber  cinereum;  Tli,  thalamus  opticus;  li,  sulcus  temj)oraiis  in- 
ferior; 7"/,  gyrus  temporalis  inferior;  t>ii,  sulcus  temporalis  medius;  Tm,  gvrus  temporalis 
medius;  ts,  sulcus  temporalis  superior;  Ts,  gyrus  temporalis  superior;  Tte,  ta?nia  lecta; 
U,  uncus;  17,  ventriculus  lateralis;  17/,  ventriculus  lateralis  (cornu  inferius);  vsl, 
pedunculus  anterior  thalami;  A",  pedunculus  putaminis;  CM,  Commissure  of  ^leynert. 


482  THE  ORGANS. 

dendrites.  By  the  Golgi  and  Ehrlich  methods,  gemmules  can  be 
demonstrated  on  the  dendrites.  The  axone  proceeds  from  the  base  of 
the  cell  (opposite  to  the  apical  dendrite)  and  usually  passes  into  the 
white  matter.  It  gives  off  several  collaterals  on  its  way  to  the  white 
matter.  (2)  Stellate  cells.  These  have  dendrites  passing  in  various 
directions.  Many,  especially  the  smaller  (granules),  m^ay  have  short 
axones  (Golgi's  second  type).  (3)  Polymorphous  cells  of  a  triangular 
or  spindle  shape  are  usually  found  in  the  deepest  layers  of  the  cortex 
and  send  their  axones  into  the  white  matter.  (4)  Horizontal  cells  (of 
Cajal),  found  in  the  outer  layer,  with  long  horizontal  dendrites  and  ax- 
ones confined  to  the  outer  layer.  (5)  Inverted  pyramidal  cells  (of 
Martinotti)  with  axones  directed  toward  the  surface.      (Fig.  325.) 

The  largest  cells  of  the  cortex  (giant  cells  of  Betz)  are  very  rich  in 
chromophilic  substance  arranged  similarly  to  that  in  the  efferent  root 
cells  of  cord  and  brain.  The  medium  and  small  cells  have  fewer 
chromophilic  bodies  which  are  often  in  the  shape  of  irregular  masses, 
either  near  the  periphery  of  the  cell  or  around  the  nucleus.  The 
neurofibrils  vary  in  their  arrangement  according  to  the  shape  of  the 
cell. 

The  neuroglia  cells  and  fibres  are  in  general  similar  to  those  in 
other  parts  of  the  nervous  system. 

The  cells  of  the  cortex  are  arranged  in  layers  which  have  the  same 
general  character  throughout,  but  in  various  regions  exhibit  variations 
such  as  suppression,  diminution,  enlargement,  or  subdivision  of  certain 
layers.  The  cell  layers  of  the  cortex  are:  (i)  Molecular  layer  (zonal 
layer,  plexiform  layer  of  Cajal).  This  contains  the  horizontal  cells, 
other  cells  with  short  axones,  and  also  receives  the  axones  of  the  Mar- 
tinotti cells.  Besides  this,  it  contains  the  terminal  branches  of  the 
apical  dendrites  of  the  pyramidal  cells.  (2)  External  granular  layer, 
very  often  termed  the  layer  of  small  pyramids.  The  dendrites  of  the 
cells  of  this  layer  mostly  enter  the  first  layer,  their  axones  pass  downward 
into  the  white  matter.  (3)  Pyramidal  layer,  often  called  the  layer  of 
superficial  medium  and  large  pyramids.  This  is  composed  principally 
of  typical  pyramids  sending  dendritic  branches  into  the  first  layer  and 
axones  into  the  white  matter.  The  larger  cells  are  in  the  deeper 
part  (sublayer  of  large  pyramids).  This  layer  also  contains  many 
granule  cells  with  short  axones  and  cells  of  Martinotti.  (4)  Internal 
granular  layer.  Here  the  predominating  elements  are  stellate  cells, 
the  larger  usually  sending  their  axones  into  the  white  matter.  Among 
these  are  many  short  axone  granules,  the  axones  of  which  end  in  the 


THE   NERVOUS   SYSTEM. 


483 


same  layer  or  in  more  superficial  layers.  (5)  Ganglionic  layer  or  deep 
layer  of  large  and  medium  sized  pyramids.  These  send  their  axones 
into  the  white  matter.  Mingled  with  them  are  short  axone  and  Marti- 
notti  Cells.     (6)  Multiform  layer  or  layer  of  polymorphous  cells.    These 


/ 

/ 


r  ■■ 


*  •*. 


''    « 


Fig.  324. — ^Vertical  Sections  of  Calcarine  .\rea  of  Adult  Human  Cortex.  Left,  W'eigert 
preparation  showing  fibre  arrangement.  Right,  Arrangement  of  cells.  (Campbell.)  G", 
Line  of  Gennari;  R,  radiary  layer;  5,  supraradiary  layer;  Z,  layer  of  superficial  tangential 
fibres  in  molecular  layer,  i,  molecular  layer;  2,  external  granular  (small  pyramid)  layer; 
3,  pyramid  layer;  4  (large  granules)  and  5  (small  granules),  internal  granular  layer;  6, 
ganglionic  layer  (containing  solitary  cells  of  Meynert);  7,  multiform  layer. 

usually  send  their  axones  into  the  w^iite  matter.     Mingled  with  them 
are  short  axone  and  Martinotti  cells.      (Figs.  324,  325  and  326.) 

The  cells  of  the  cortex  obviously  fall  into  two  classes:  efferent projec- 
iion  cells  and  association  cells.  Which  cells  are  projection  cells  is  not 
definitely  known,  except  in  the  case  of  the  preccntral  motor  cortex 


484 


THE  ORGANS. 


Ill 


Fig.  325. 


where  it  has  been  estab- 
lished that  these  cells  are 
the  cells  of  Betz,  the  axones 
of  which  form  the  pyra- 
midal tract.  An  examina- 
tion of  this  area  shows  that 
the  association  cells  must 
enormously  outnumber  the 
efferent  projection  cells  in 
the  cortex.  The  association 
cells  comprise  the  short 
axone    cells    and   cells    the 


Fig.  325. — Vertical  section  of 
Calcarine  Area  of  Cortex  of  an 
Infant  15-20  days  old.  (Cajal, 
combined  from  three,  /,  //  and 
///,  somewhat  overlapping  figures. 
The  multiform  layer  is  not  in- 
cluded).    Golgi's  method. 

/. — A,  Molecular  layer;  B, 
external  granular  layer  (of  small 
pyramids);  C,  pyramidal  layer  (of 
medium  pyramids);  a,  descending 
axones;  h,  ascending  collaterals;  c, 
apical  dendrites  of  large  pyramidal 
cells  in  ganglionic  layer. 

II. — A,  Sublayer  of  large 
stellate  cells;  B,  sublayer  of  small 
stellate  cells;  C,  outer  part  of 
ganglionic  layer;  a.  crescentic 
stellate  cells;  h,  and/,  horizontal, 
spindle-shaped  stellate  cells;  c, 
medium-sized  pyramidal  cells;  e, 
stellate  cells  with  arched  axones; 
g,  triangular  stellate  cells  with 
stout,  arched  collaterals;  h,  pyra- 
midal cells  with  arched  axones. 

III. — A,  Part  of  internal 
granular  layer;  B,  sublayer  of  small 
pyramidal  cells  with  arched  as- 
cending axones;  C,  sublayer  of 
large  pyramids;  a,  large  pjyramidal 
cell;  b,  medium-sized  pyramidal 
cell  with  lo.g  descending  axone; 
c,  small  pyramidal  cell  with  arched 
ascending  axone;  d,  pyramidal  cell 
with  axone  split  into  two  arched 
ascending  branches;  e,  pyramidal 
cells  whose  axone  sends  out  various 
ascending  branches;  f,g,h,  stellate 
cells  with  ascending  axones  which 
branch  in  B  and  in  the  sublayer 
of  small  stellate  cells;  i,j,k,  pyra- 
midal cells  with  arched  ascending 
axones  which  send  branches  into 
the  ganglionic  layer. 


THE  NERVOUS   SYSTEM.  485 

fibres  of  which  enter  the  white  matter,  but  terminate  in  some  other 
part  of  the  cortex  forming  the  association  fibres  of  the  white  matter. 
(Compare  p.  479.) 

It  is  thus  evident  that  every  part  of  the  cortex  contains  terminations 
of  association  fibres.  The  areas  containing  the  terminations  of  aft'er- 
ent  projection  fibres  are  those  which  receive  the  thalamocortical  con- 
tinuations of  the  afferent  pallial  paths  and  the  continuations  of  the 
olfactory  paths.  From  observations  made  with  the  Golgi  method 
it  seems  probable  that  the  latter  are  represented  by  coarse  fibres 
which  may  ramify  throughout  the  greater  part  of  the  thickness  of  the 
cortex,  but  are  confined  mainly  to  the  third  and  fourth  layers.  The 
principal  areas  of  the  cortex  receiving  the  afferent  projection  fibres 
are  the  olfactory  hippocampal  area,  the  calcarine  (visual)  area  (fibres 
from  lateral  geniculate  body),  the  transverse  temporal  gyri  of  Heschl 
(auditory  fibres  from  medial  geniculate  body),  and  the  pre-  and  post- 
central areas  (postcentral  only,  according  to  some  authorities — area 
of  general  sensation  from  body  and  head — fibres  from  ventrolateral 
thalamic  nuclei).      (Fig.  327.) 

The  medullated  fibres  of  the  cortex  consist  of  radially,  obliquely, 
and  tangentially  running  fibres.  The  radial  fibres  enter  the  cortex 
from  the  white  matter  in  bundles  known  as  the  radiations  of  Meynert 
which  extend  a  variable  distance  toward  the  periphery,  diminishing 
until  they  end  usually  in  the  third  layer.  They  consist  mainly  of  the 
axones  of  the  adjoining  cells  passing  to  the  white  matter.  Their 
fibres  are  of  varying  caliber,  the  coarsest  originating  from  the  largest 
cells.  The  oblique  fibres  form  a  dense  plexus  of  coarse  and  fine  fibres 
between  the  radial  fibres,  the  interradiary  plexus.  Toward  the 
surface  (in  the  second  and  third  cell  layers)  they  form  a  delicate  plexus 
of  fine  fibres.  This  latter  plexus  lies  principally  superficial  to  the 
radiations  of  Meynert  and  is  the  siipraradiary  plexus.  A  denser 
aggregation  of  irregular  fibres  constitutes  the  line  or  stria  of  Baillarger 
located  in  the  layer  of  superficial  large  pyramids.  It  is  probable  that 
this  represents  a  layer  especially  rich  in  terminals  of  fibres  from  the 
white  matter.  Other  striae  are  also  described.  Besides  representing 
the  terminals  of  such  fibres  the  oblique  fibres  in  general  are  also  com- 
posed of  medullated  collaterals  of  axones  of  pyramids  and  possibly  ar- 
borizations of  short  axone  cells.  A  few  coarser  fibres  ascending  to  the 
molecular  layer  are  ascending  fibres  from  Martinotti  cells.  The  deep 
tangential  fibres,  most  marked  on  the  sides  of  the  con\"olutions  and 
in  the  sulci,  are  considered  short  association  fibres  belonging  to  the 


THE  ORGANS. 


-/•:' 


r.A- 


i.^^.v 


•I  w 


'i  ■  i- 


•  i   ■ 


/■i' 


Fig.  326. — Vertical  Sections  of  Precentral  or  Motor  Area  of  Adult  Pluman  Cortex. 
Left,  Weigert  preparation  .showing  fibre  arrangement.  Right,  Arrangement  of  cells. 
(Campljell.j  B,  Position  of  line  of  Baillarger,  its  position  obscured  by  surrounding  wealth 
of  fibres;  R,  radiary  layer;  .V,  supraradiary  layer;  Z,  layer  of  superficial  tangential  fibres 
in  molecular  layer,  flense  and  well  defined;  i,  molecular  layer;  2,  external  granular  layer 
(small  pyramids),  3  (medium-sized)  and  4  (large),  pyramid  layer;  5,  internal  granular  layer, 
indistinct  and  with  scatterefl  granule  or  stellate  cells;  6,  ganglionic  layer  (large  deep  pyra- 
mids); 7,  multiform  layer. 


THE   NERVOUS   SYSTEM. 


487 


,'  P,.«n^..!  posl'"'  ^.P0'"=- 


■psychic 


Visuo-xnsorjf 


^uditO'sensory 


■X'.t^^" 


//     / 


II 


Fig.  327. — Diagram  (orthogonal)  showing  Cortical  Areas  as  determined  bv  the 
Arrangement  and  Distribution  of  Fibres  and  Cells  (A.  W.  Campbell).  Large  portions 
of  important  areas  are  concealed  within  fissures,  e.g.  the  calcarine  or  visual  {visuo-sen- 
sory,  within  the  calcarine  fissure)  precoitral  (motor)  and  postcentral  (within  the  fissure  of 
Rolando)  and  especially  the  acoustic  {aitdito-sensory)  which  is  almost  completely  hidden 
within  the  Sylvian  fissure.     A,  B  and  C,  parts  of  the  limbic  lobe. 


488  THE  ORG.^NS. 

fibrffi  propriae  of  Meynert.  In  the  molecular  layer  are  the  superficial 
tangential  fibres  consisting  of  the  axones  of  the  horizontal  cells  and  the 
terminals  of  the  axones  of  Martinotti  cells.     (Figs.  324  and  326.) 

The  cortex  is  divided  into  various  areas  by  various  investigators, 
the  areas  being  distinguished  (a)  by  the  time  of  medullation  (myelo- 
genetic  method  of  Flechsig),  {h)  by  the  number  and  arrangement  of  the 
meduUated  fibres  (myeloarchitecture),  especially  the  number,  thickness, 
and  distinctness  of  the  striae,  such  as  that  of  Baillarger,  formed  by  them 
and  (c)  by  the  number  and  arrangement  of  the  cells  (cy toarchitecture) . 
Many  such  areas  have  been  thus  distinguished  by  different  investigators 
with  results  agreeing  in  many  respects  but  differing  in  others.  The 
areas  most  clearly  defined  and  concerning  which  there  is  perhaps  the 
most  general  agreement  are  the  various  sensory  (afferent  projection) 
areas  already  enumerated  (p.  485)  and  the  motor  (efferent  projection) 
precentral  area  (Fig.  327).  These  areas  myelinate  first  (at  or  soon 
after  birth),  next  areas  adjacent  to  them,  and  last  areas  occupying 
a  considerable  portion  of  the  human  pallium  but  much  less  extensive 
in  other  mammals.  There  is  much  difference  of  opinion  as  to  the 
extent  to  which  these  last  myelinating  areas  are  supplied  with  pro- 
jection fibres.  xA.ccording  to  some  authorities  the  areas  myelinating 
last  have  no  projection  fibres  and  are  consequently  entirely  composed 
of  association  cells  and  fibres.  Perhaps  the  two  best-marked  of  the 
various  areas  are  the  motor  and  visual  areas  the  structure  of  which  is 
shown  in  figures  324,  325  and  326.  The  motor  precentral  cortex  is 
characterized  by  the  presence  of  the  giant  cells  of  Betz,  by  an  almost 
complete  absence  of  an  internal  granular  layer  and  by  a  great  wealth  of 
fibres.  The  calcarine  or  visual  area  is  characterized  by  a  strongly 
marked  line  of  Gennari  (  =  Baillarger)  and  by  a  double  or  triple 
internal  granular  layer  containing  large  granules  in  place,  apparently, 
of  the  superficial  large  pyramids.  The  line  of  Gennari  is  probably 
partly  composed  of  the  terminals  of  the  optic  path. 

TECHNIC. 

(i)  The  general  structure  of  the  cerebellum  is  well  brought  out  by  staining 
sections  of  formalin-MuUcr's  fluid-iixed  material  with  hiematoxylin-picro-acid- 
fuchsin  ftechnic  3,  p.  19),  and  mounting  in  balsam. 

(2)  The  arrangement  of  the  cell  layers  of  both  cerebellum  and  cerebrum,  as 
well  as  certain  details  of  internal  structure  of  the  cells,  can  be  studied  in  sections 
of  alcohol-  or  formalin-fixed  material  stained  by  the  method  of  Nissl  (technic, 
P-  35 J- 


THE  NERVOUS   SYSTEM.  489 

(3)  The  distribution  of  the  medullated  nerve  fibres  of  either  the  cerebellar  or 
cerebral  cortex  is  best  demonstrated  by  fixing  material  in  Miiller's  fluid  (technic  4, 
p.  6)  or  in  formalin-Miiller's  fluid,  and  staining  rather  thick  sections  by  the  Wei- 
gert  or  Weigert-Pal  method  (technic,  p.  29). 

(4)  The  external  morphology  of  the  cerebellar  and  cerebral  neurones  and  the 
relations  of  cell  and  fibre  can  be  thoroughly  understood  only  by  means  of  sec- 
tions stained  by  one  of  the  Golgi  methods  (technic,  pp.  32  and  ^^).  Especially  in 
the  case  of  the  cerebellum,  sections  should  be  made  both  at  right  angles,  and  longi- 
tudinal to  the  long  axis  of  the  convolution.  Golgi  preparations  from  embryonic 
material  and  from  the  brains  of  lower  animals  furnish  instructive  pictures. 

(5)  The  silver  method  of  Cajal  should  be  used,  especially  with  alcohol  fixa- 
tion (technic  p.  34,  No.  2),  both  for  the  neurofibrils  and  for  the  external  mor- 
phology of  the  neurones.     It  is  especially  successful  with  the  cerebellum. 

(6)  Neuroglia  stains  should  also  be  used. 


The  Pituitary  Body. 

The  pituitary  body  or  hypophysis  cerebri  consists  of  two  lobes 
which  are  totally  different  both  in  structure  and  in  origin. 

The  Anterior  Lobe. — This  is  the  larger,  and  is  glandular  in 
character.  It  is  of  ectodermic  origin,  developing  as  a  diverticulum 
from  the  primitive  oral  cavity.  Its  mode  of  development  is  that  of 
a  compound  tubular  gland,  the  single  primary  diverticulum  undergoing 
repeated  division  to  form  the  terminal  tubules.  The  original  diver- 
ticulum ultimately  atrophies  and  disappears,  leaving  the  gland  en- 
tirely unconnected  with  the  surface.  The  gland  is  enclosed  in  a 
connective-tissue  capsule,  from  which  trabeculae  pass  into  the  organ 
forming  its  framework.  The  gland  cells  are  arranged  in  slightly 
convoluted  tubules  and  rest  upon  a  basement  membrane.  Between 
the  tubules  is  a  vascular  connective  tissue.  Some  of  the  gland  cells 
are  small  cuboidal  cells  with  nuclei  at  their  bases  and  a  finely  granular 
basophile  protoplasm  {chief  cells).  Others,  somewhat  less  numerous 
than  the  preceding,  are  larger  polygonal  cells  with  centrally  placed  nu- 
clei and  protoplasm  containing  coarse  acidophile  (eosinophile)  granules 
(chromophile  cells).  While  presenting  different  appearances  and  usu- 
ally described  as  two  kinds  of  cells,  it  is  probable  that  chromophile 
cells  and  chief  cells  represent  merely  different  functional  conditions  of 
the  same  cell.  Some  alveoli  in  the  posterior  portion  of  the  lobe  fre- 
quently contain  a  colloid  substance  similar  to  that  found  in  the  thyreoid. 

As  in  all  ductless  glands,  the  blood  supply  is  rich  and  the  rela- 
tions of  capillaries  to  gland  cells  are  extremely  intimate,  dense  net- 
works of  capillaries  surrounding  the  alveoli  on  all  sides. 


490  THE  ORGANS. 

The  Posterior  Lobe. — This,  like  the  anterior,  is  surrounded  by 
a  connective-tissue  capsule  which  sends  trabeculse  into  its  substance. 
In  the  human  adult  the  lobe  consists  mainly  of  neuroglia  with  a  few 
scattered  cells,  which  probably  represent  rudimentary  ganglion  cells. 
In  the  human  embryo,  and  in  many  adult  lower  animals,  the  nervous 
elements  are  much  more  prominent  and  more  definitely  arranged. 
Thus  Berkley  describes  the  posterior  lobe  of  the  pituitary  body  of  the 
dog  as  consisting  of  three  distinct  zones:  (i)  An  outer  zone  of  three 
or  four  layers  of  cells  resembling  ependymal  cells,  connective-tissue 
septa  from  the  capsule  separating  the  cells  into  irregular  groups;  (2) 
A  middle  zone  of  glandular  epithelium,  some  of  the  cells  of  which  are 
arranged  as  rather  indefinite  alveoli  which  may  contain  colloid.  This 
is  termed  the  pars  intermedia.  The  epithelial  cells  are  derived  from 
the  oral  invagination.  (3)  An  inner  layer  of  nerve  cells  and  neuroglia 
cells.  These  react  to  the  Golgi  stain,  the  nerve  cells  having  axones 
and  dendrites.  Most  of  the  axones  appeared  to  pass  in  the  direction 
of  the  infundibulum,  but  could  not  be  traced  into  the  latter.  The 
posterior  lobe  is  of  ectodermic  origin,  developing  as  a  diverticulum  from 
the  floor  of  the  third  ventricle.  The  remains  of  the  diverticulum  con- 
stitute the  infundibulum. 


The  Pineal  Body. 

The  pineal  body  originates  as  a  fold  of  the  wall  of  the  primary 
brain  vesicle.  It  lies  upon  the  dorsal  surface  of  the  inter-  and 
mid-brain,  ?jeing  connected  with  the  former.  The  pineal  body  is  ap- 
parently of  the  nature  of  a  rudimentary  sense  organ,  being  some- 
times referred  to  as  the  median  or  pineal  eye.  In  man  it  is  surrounded 
by  a  firm  connective-tissue  capsule,  which  is  a  continuation  of  the  pia 
mater.  This  sends  trabeculse  into  the  organ,  which  anastomose  and 
divide  it  into  many  small  chambers.  The  latter  contain  tubules  or 
alveoli  lined  with  cuboidal  epithelium.  This  may  be  simple  or  strati- 
fied, and  frequently  almost  completely  fills  the  tubules.  Within  the 
tubules  are  often  found  calcareous  deposits  known  as  "brain  sand." 

TECHNIC. 

The  general  structure  of  the  pituitary  body  and  of  the  ])ineal  body  can  be 
studied  by  fixing  material  in  formalin-Muller's  fluid  (technic  5,  p.  7)  and  staining 
sections  with  ha;matoxyIin-eosin  ("technic  t,  p.  t8). 


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THE  NERVOUS   SYSTEM.  493 

General  References  for  Further  Study. 

Bailey  and  Miller:  A  Text-book  of  Embryology,  Xew  York,  1909.  Chaps. 
XVII  and  XVIII. 

Barker:  The  X'ervous  System  and  its  Constituent  Neurones,  New  York,  1899. 

Dejerine:  Anatomie  des  centres  nerveux,  Paris,  1895. 

Edinger,  L.:  Vorlesungen  iiber  den  Bau  der  nervosen  Zentralorgane  des 
Menschen  und  der  Tiere,  Leipsig,  1904. 

Van  Gehuchten:  Anatomie  du  systeme  nerveux  de  I'homme,  Louvaine,  1906. 

Golgi:  Untersuchungen  iiber  den  feineren  Bau  des  centralen  und  peripher- 
ischen  Nervensystems,  Jena,  1894. 

Johnston,  J.  B.:  The  Nervous  System  of  Vertebrates,  1906. 

Kolliker:  Handbuch  der  Gewebelehre  des  Menschen,  Leipsic,  1896. 

Von  Lenhossek:  Der  feinere  Bau  des  Nervensystems  im  Lichte  neuester  For- 
schungen,  Berlin,  1895. 

Marburg:  Atlas  des  menschlichen  Centralnervensystems,  Leipzig  and  Wien, 
1910. 

Meyer,  Adolf:  Critical  Review  of  the  Data  and  General  Methods  and  De- 
ductions of  Modern  Neurology.  Joiini.  of  Comp.  Neurol.,  Vol.  VIII.  X'os.  3 
and  4,  1898. 

Obersteiner:  Anleitung  beim  Studieren  des  Baues  der  nen-osen  Centralorgane, 
Leipsic. 

Quain's  Elements  of  Anatomy,  Vol.  Ill,  Neurology,  Parts  i  and  2,  1908. 

Ramon  yCajal:  Beitrag  zum  Studium  der  Medulla  Oblongata,  etc.,  Leipsic, 
1896.^ — Les  nouvelles  idees  sur  la  structure  du  systeme  nerveux  chez  I'homme  et 
chez  les  vertebres,  Paris,  1894. — Textura  del  sistema  nervioso  del  hombre  v  de 
los  vertebrados,  Madrid  1899-1904  (contains  many  illuminating  figures). — Studien 
iiber  die  Hirnrinde  des  Menschen,  Leipsig,  1900. 

Spalteholz,  W. :  Handatlas  of  Human  Anatomy  (trans,  by  L.  F.  Barker) 
Vol.  Ill,  1903. 


CHAPTER  XII. 
THE  ORGANS  OF  SPECIAL  SENSE. 

The  Organ  of  Vision. 

The  eyeball  and  optic  nerve  constitute  the  organ  of  vision.  To 
be  described  in  connection  with  them  are  the  eyelid  and  the  lacrymal 
apparatus. 

The  Eyeball  or  Bulbus  Oculi. — This  is  almost  spherical,  although 
slightly  flattened  antero-posteriorly.  It  consists  of  a  wall  enclosing  a 
cavity  filled  with  fluid. 

The  wall  of  the  eyeball  consists  of  three  coats:  (a)  An  external 
fibrous  coat — the  sclera  and  cornea;  (b)  a  middle  vascular — the  cho- 
rioid;  and  (c)  an  internal  nervous — the  retina  (Fig.  328). 

The  Sclera  (Figs.  328  and  329). — This  consists  of  dense  fibrous 
tissue  with  some  elastic  fibres.  The  fibres  run  both  meridionally 
and  equatorially,  the  tendons  of  the  straight  muscles  of  the  eyeball 
being  continuous  with  the  meridional  fibres,  those  of  the  obUque 
muscles  with  the  equatorial  fibres.  The  few  cells  of  the  sclera  lie 
n  distinct,  very  irregular  cell  spaces,  and  frequently  contain  pigment 
granules.  Pigmented  cells  in  considerable  numbers  are  regularly 
present  near  the  corneal  junction,  at  the  entrance  of  the  optic  nerve, 
and  on  the  inner  surface  of  the  sclera.  Where  the  optic  nerve  pierces 
the  sclera,  the  continuity  of  the  latter  is  broken  by  the  entering  nerve 
fibres,  forming  the  lamina  cribosa  (Fig.  337).  The  pigmented  layer 
of  the  sclera  next  the  chorioid  is  known  as  the  lamina  fusca,  and  is 
lined  internally  by  a  single  layer  of  flat  non-pigmented  endothelium. 
Anteriorly  a  loose  connective  tissue  attaches  the  sclera  to  the  scleral 
conjunctiva. 

The  Cornea  (Figs.  330  and  Zo2>)- — This  is  the  anterior  continua- 
tion of  the  sclera  so  modified  as  readily  to  allow  the  light  to  pass 
through  it.  It  is  about  i  mm.  thick  and  consists  of  five  layers,  which 
from  before  backward  are  as  follows  (Fig.  330) : 

ii)  Anterior  epithelium. 

{2)  Anterior  elastic  membrane  or  memljrane  of  Bowman. 

(3)  Substantia  propria  corneas. 

494 


THE  ORGANS  OF  SPECIAL  SENSE. 


495 


(4)  Posterior  elastic  membrane  or  membrane  of  Descemet. 

(5)  Posterior  endothelium  or  endothelium  of  Descem.et. 

(i).The  anterior  epithelium  (Fig.  330J,  i)  is  of  the  stratified  squa- 
mous type  and  consists  of  from  four  to  eight  layers  of  cells.  The 
deepest  cells  are  columnar  and  rest  upon  the  anterior  elastic  mem- 
brane. The  middle  cells  are  polygonal  and  are  connected  by  short 
intercellular  bridges.     The  surface  cells  are  fiat.     Along  the  margin 


Fig.  328. — Diagram  of  Eyeball  showing  Coats.  (Merkel-Henle.)  a.  Sclera;  b, 
chorioid;  c,  retina;  d,  cornea;  e,  lens;/,  iris;  g,  conjunctiva;  h,  ciliary  body;  /,  sclero-corneal 
junction  and  canal  of  Schlemm;  j,  fovea  centralis;  tz,  optic  nerve. 


of  the  cornea  the  epithelium  is  continuous  with  that  of  the  conjunc- 
tiva (Fig.  zZo)- 

(2)  The  anterior  elastie  membrane  (Fig.  330,  2)  is  a  highly  de\elopcd 
basement  membrane,  its  anterior  surface  l^eing  pitted  to  receive 
the  bases  of  the  deepest  epithelial  cells.  It  is  apparently  homo- 
geneous, and  while  called  an  elastic  membrane,  does  not  conform 
chemically  to  either  fibrous  or  elastic  tissue.  By  means  of  special 
technic,  a  fibrillar  structure  has  l)cen  demonstrated. 


496 


THE  ORGANS. 


(3)  The  subslaniia  propria  (Fig.  330,  3)  constitutes  the  main 
bulk  of  the  cornea.  It  consists  of  connective  tissue  the  fibrils  of  which 
are  doubly  refracting  and  are  cemented  together  to  form  bundles 
and  lamellae.  In  the  human  cornea  the  lamellae  are  about  sixty  in 
number.  The  lamellae  are  parallel  to  one  another  and  to  the  sur- 
face of  the  cornea,  but  the  fibres  of  adjacent  lamellae  cross  one  another 
at  an  angle  of  about  twelve  degrees.  The  lamellae  are  united  by 
cement  substance.  Fibres  running  obliquely  through  the  lamellae 
from  posterior  to  anterior  elastic  membranes  hold  the  lamellae  firmly 
together.     They  are  known  as  perforating  or  arcuate  fibres. 


^iAraMj.^v>YtoaHt,ig-iy.fc^:^iF^^^ 


c 


Fig.  329. — Vertical  Section  through  Sclera,  Chorioid,  and  Pigment  Layer  of  Retina. 
(Merkel-Henle.)  A,  Sclera;  B,  chorioid;  C,  pigment  layer  of  retina;  d,  lamina  supra- 
chorioidea;  e,  Haller's  layer  of  straight  vessels;/,  choriocapillaris;  g,  vitreous  membrane. 


Between  the  lamellae  are  irregular  flat  cell  spaces  which  commu- 
nicate with  one  another  and  with  the  lymph  spaces  at  the  margin  of 
the  cornea  by  means  of  canalicuh.  Seen  in  sections  vertical  to  the 
surface  of  the  cornea,  these  spaces  appear  fusiform.  In  the  spaces  are 
the  connective-tissue  cells  of  the  cornea  or  corneal  corpuscles.  These 
are  fiat  cells  corresponding  in  shape  to  the  spaces  and  sending  out 
processes  into  the  canaliculi  (Figs.  331  and  332). 

(4)  The  posterior  elastic  membrane  or  membrane  of  Descemet 
(Fig.  330,  4)  resembles  the  anterior,  but  is  much  thinner.  Like 
the  anterior,  it  docs  not  give  the  chemical  reaction  of  elastic  tissue. 

(5)  The  posterior  endothelium  or  endothelium  of  Descemet  (Fig. 
330,  5j  consists  of  a  single  layer  of  flat  hexagonal  cells,  the  nuclei 
of  which  frequently  project  slightly  above  the  surface. 

The  cornea  contains  no  blood-vessels. 

The  Chorioid. — This  is  made  up  of  four  layers  which  from 
without  inward  are  as  follows  (Fig.  329J : 


THE  ORGANS  OF  SPECIAL  SENSE. 


497 


(i)  The   lamina   suprachorioidea. 

(2)  The  layer  of  straight  vessels — Haller's  layer. 

(3)  The  capillary  layer — choriocapillaris. 

(4)  The  vitreous  membrane — lamina  citrea — membrane  of  Bruch. 

(i)  The  lamina  suprachorioidea  (Fig.  329,  d)  is  intimately  con- 
nected with  the  lamina  fusca  of  the  sclera  and  consists  of  loosely 
arranged  bundles  of  fibrous  and  elastic  tissue  among  which  are  scat- 
tered pigmented  and  non-pigmented 
connective-tissue  cells.  Numerous 
lymph  spaces  are  found  between  the 
bundles  of  connective  tissue  and  be- 
tween the  lamina  suprachorioidea  and 
lamina  fusca.  The  latter  are  known 
as    the    perichorioidal    lymph    spaces 

(Fig-  ZZZ)- 

(2)  The   layer   of  straight   vessels 

(Fig.  329,  e)  consists  of  tibro-elastic 
tissue  containing  numerous  pigmented 
and  non-pigmented  cells,  supporting 
the  large  blood-vessels  of  the  layer. 
The  latter  can  be  seen  with  the 
naked  eye,  and,  running  parallel 
straight  courses,  give  to  the  layer  a 
striated  appearance.  The  arteries  lie 
to  the  inner  side.  The  veins  which 
are  larger  than  the  arteries  converge 
toward  four  points — vencB  vorticos(2 — 
one  in  each  quadrant  of  the  eyeball. 

A  narrow  boundary  zone,  rich  in 
elastic  fibres  and  free  from  pigment, 

limits  this  layer  internally.  It  is  much  more  highly  developed  in 
some  of  the  lower  animals  than  in  man.  Formed  of  connective- 
tissue  bundles  in  ruminants  and  horses,  it  is  known  as  the  tape  turn 
fibrosum,  while  in  the  carnivora  its  structure — several  layers  of  fiat  cells 
— gives  it  the  name  of  the  ta petit m  cellulosum. 

(3)  The  choriocapillaris  (Fig.  329,  /)  consists  of  connective  tissue 
supporting  a  dense  network  of  capillaries,  which  is  most  dense  in  the 
region  of  the  macula  lutca.  This  layer  is  usually  described  as  free 
from  pigment,  although  it  not  infrequently  contains  some  |)iu;mentcd 
cells. 


Fig.  330. — ^\'ertical  Section  of  Cornea. 
(Merkel-Henle.)  i,  Anterior  epi- 
thelium; 2,  anterior  elastic  mem- 
brane; 3,  substantia  propria  corner; 
4,  posterior  elastic  membrane;  5, 
posterior  endothelium. 


498 


THE  ORGANS. 


(4)  The  vitreous  membrane  (Fig.  329,  g)  is  a  clear,  apparently  struc- 
tureless membrane  about  two  microns  thick.  Its  outer  surface  is 
grooved  by  the  capillaries  of  the  choriocapillaris,  while  its  inner  surface 
is  pitted  by  the  retinal  epithelium. 


'  ^  >*i' ,-?.•'         V.^     -^if-f- 


■^  M: 


12^ 


Fig.  331. — Section  of  Human  Cornea  cut  Tangential  to  Surface—  X350  (technic  9,  p.  81)  — 
showing  corneal  cell  spaces  (lacunae)  and  anastomosing  canaliculi. 

The  Ciliary  Body. — This  is  the  anterior  extension  of  the  chorioid 
and  consists  of  the  ciliary  processes  and  the  ciliary  muscle  (Fig.  333). 
It  extends  from  the  ora  serrata  (a  wavy  edge  which  marks  the  anterior 


■/  - 


•*^  *>>j?^'''"*"''  *'    "■' 


/    ?' 


.•'<, 


f-t: 


'"''Zl.x^ 


Fig.  332. — Section  of  Human  Cornea  cut  Tangential  to  Surface — X350  (technic  8,  p.  81) — 
shcjwing  corneal  ceils  and  their  anastomosing  processes. 

limit  of  the  nervous  elements  of  the  retina — see  Retina)  to  the  margin 
of  the  iris  (see  below). 

The  ciliary  processes  (Fig.  2)2)2)) y  f^^-*"^  seventy  to  eighty  in  number, 


THE  ORGAXS  OF  SPECIAL  SEXSE. 


499 


are  meridionally-running  folds  of  the  chorioid  from  which  are  given 
off  numerous  irregular  secondary  folds.  The  processes  begin  low 
at  the  ora  serrata,  gradually  increase  in  height  to  about  i  mm.,  and  end 
abruptly  at  the  margin  of  the  iris.  The  ciliary  processes  consist  of 
connective  tissue  containing  many  pigmented  cells  and  supporting 
numerous  blood-vessels.  Invaginations  lined  with  clear  columnar 
epithelium  have  been  described  as  ciliary  glands.     The  ciliary  folds 


f  i   III!  I|i 
'ill! P  ''■ 

Anterio? chamber — S,  .  /';'-, 


Canal  of  Schlemm — i^ 
Spaces  of  Fontana 


Conjunctiva 


Iris 

Pars  iridica  retiose 


^^  Ciliary  process 

^^jV;        Ligamentum 


;  ,^,  .      ~r^        pectinatum  iridU 

'    iSS%-^-^! Circular  fibres 

of  ciliary  muscle 


Radial  fibres  of 
ciliary  muscle 


Pars  ciliaris  retinas 


Pericliorioidal  lymph  space. 


Fig.  3^^. — Vertical  Section  through  Human  Sclero-corneal  Junction.     (Cunningham.) 


are  covered  by  the  vitreous  membrane,  and  internal  to  the  latter  is  a 
continuation  forward  of  non-nervous  elements  of  the  retina — pars 
ciliaris  retina  (Fig.  ^2>2>)-  This  consists  of  two  layers  of  columnar 
epithelial  cells,  the  outer  layer  being  pigmented,  the  inner  non- 
pigmented. 

The  ciliary  muscle  (Fig.  t^t^t^)  is  a  band  of  smooth  muscle  which 
encircles  the  iris.  It  lies  in  the  outer  anterior  part  of  the  ciliary  body, 
and  on  cross  section  has  a  generally  triangular  shape.  It  is  divisible 
into  three  groups  of  muscle  cells:  {a)  An  inner  circular  group  near 
the  base  of  the  iris — circular  muscle  of  Midler;  [b)  an  outer  meridional 


500 


THE  ORGANS. 


^^S53 


group  lying  next  to  the  sclera  and  known  as  the  tensor  chorioideae, 
and  (c)  a  middle  radial  group.  The  meridional  and  radial  groups 
both  take  origin  in  the  posterior  elastic  lamina  of  the  cornea,  the  former 
passing  backward  along  the  margin  of  the  sclera  to  its  insertion  in  the 
ciliary  body  near  the  ora  serrata,  the  latter  radiating  fan-like  to  a 
broad  insertion  in  the  ciliary  body  and  processes. 

The  ciliary  body  is  closely  attached  to  the  sclero-corneal  junction 
by  the  ligamentum  pectinatum  (Fig.  333),  a  continuation  of  the  posterior 
elastic  lamina  of  the  cornea.     Within  the  ligament  are  spaces  {spaces 

of  Fontana)  lined  with  endothelium. 
These  are  apparently  lymph  spaces, 
and  communicate  with  each  other, 
with  similar  spaces  around  the  canal 
of  Schlemm,  and  with  the  anterior 
chamber.  The  canal  of  Schlemm 
(Fig.  333)  is  a  venous  canal  which 
encircles  the  cornea,  lying  in  the 
sclera  close  to  the  corneal  margin. 
Instead  of  a  single  canal  there  may 
be  several  canals. 

The  Iris  (Fig.  334). — This  rep- 
resents a  further  continuation   for- 
ward of   the   chorioid.      Its  base  is 
attached    to    the    ciliary   body    and 
ligamentum  pectinatum.     From  this 
point  it  extends  forward  as  a  dia- 
phragm   in    front    of    the    lens,    its 
centre  being  perforated  to  form  the 
pupillary  opening.     It  is  deeply  pig- 
mented, and  to  its  pigment  the  color  of  the  eye  is  due.     Four  layers 
may  be  distinguished,  which  from  before  backward  are  as  follows : 
fi)  The  anterior  endothelium. 

(2)  The  stroma. 

(3)  The  vitreous  membrane. 

(4)  The  pigmented  ei^ithelium.. 

({)  The  anterior  endothelium  is  a  single  layer  of  pigmented  cells 
continuous  with  the  posterior  endothelium  of  the  cornea  (Fig.  334,  a). 

(2)  The  stroma  is  divisible  into  two  layers:  an  anterior  reticular 
layer,  containing  many  cells,  some  of  which  are  ])igmented,  and  a 
vascular  layer,  the  vessels  of  which  are  ])eculiar  in  that  their  walls  con- 


FlG.  334. — Vertical  Section  through 
Iris.  (Merkel-Henle.)  a,  Anterior 
endothelium;  b,  stroma  or  substantia 
propria;  c,  vitreous  membrane;  d, 
pigment  layer;  v,  blood-vessel. 


THE  ORGANS  OF  SPECIAL  SENSE.  501 

tain  almost  no  muscle,  but  have  thick  connective-tissue  sheaths.  In 
the  posterior  part  of  the  stroma  are  bundles  of  smooth  muscle.  Those 
nearest  the  pupillary  margin  encircle  the  pupil  forming  its  sphincter 
muscle,  while  external  are  scattered  radiating  bundles  forming  the 
dilator  muscle. 

(3)  The  vitreous  membrane  is  continuous  with,  and  has  the  same 
structure  as  the  membrane  of  Bruch. 

(4)  The  pigmented  epithelium  (Fig.  334,  d)  consists  of  several  layers 
of  cells  and  is  continuous  with  the  pars  ciliaris  retinae.  Except  in 
albinos,  both  layers  are  pigmented. 

The  Retina. — The  retina  is  the  nervous  tunic  of  the  eye.  It 
lines  the  entire  eyeball,  ending  only  at  the  pupillary  margin  of  the 
iris.  Its  nervous  elements,  however,  extend  only  to  the  or  a  serrata, 
which  marks  the  outer  limit  of  the  ciliary  body  (Fig.  ^,^5).  The 
nervous  part  of  the  retina  is  known  as  the  pars  optica  retina,  the 
non-nervous  extension  over  the  ciliary  processes  as  the  pars  ciliaris 
retina,  its  further  continuation  o^•er  the  iris  as  the  pars  iridica  retina. 
Modifications  of  the  optic  portion  of  the  retina  are  found  in  the  region 
of  the  macula  lutea  and  of  the  optic  nerve  entrance. 

The  Pars  Optica  Retina. — This  is  the  only  part  of  the  retina 
directly  concerned  in  the  reception  of  impulses,  and  may  be  regarded 
as  the  extremely  complex  sensory  end-organ  of  the  optic  nerve.  It 
is  divisible  into  ten  layers,  which  from  without  inward  are  as  follows 
(Fig-  roS)  ■ 


(i)  Layer  of  pigmented  epithelium. 
(2)  Layer  of  rods  and  cones. 


Layer  of  neuro-epithelium. 


Ganglionic  lavcr. 


The  layer  of  pigmented  epithelium  (Fig.  335,  B,  i)  consists  of  a 
single  layer  of  regular  hexagonal  cells  (Fig.  25,  p.  69).  The  nuclei 
lie  in  the  outer  part  of  the  cell,  while  from  the  inner  side  thread-like 
projections  extend  down  lu'twecn  the  rods  and  cones  of  the  layer  next 
internal.     The   pigment   has   the   form   of  rod-shaped   granules.     Its 


(3) 

Outer  limiting  membrane. 

(4) 

Outer  nuclear  layer. 

(5) 

Outer  molecular  layer. 

(6) 

Inner 

nuclear  layer. 

(7) 

Inner 

molecular  layer. 

(8)  Layer 

of  nerve  cells. 

(9)  Layer 

of  nerve  fibres. 

(10) 

Inner 

limiting  membrane. 

502 


THE  ORGANS. 


distribution  seems  to  depend  upon  the  amount  of  light  being  admitted 
to  the  retina.  When  Httle  or  no  Hght  is  being  admitted,  the  pigment 
is  found  in  the  body  of  the  cell,  the  processes  being  wholly  or  almost 
free  from  pigment;  when  the  retina  is  exposed  to  a  bright  light,  some  of 
the  pigment  granules  pass  down  into  the  processes  so  that  the  pig- 
ment becomes  more  evenly  distributed  throughout  the  cell. 


Fig.  335. — A,  Scheme  of  retina  as  shown  by  the  Golgi  method.  B,  Vertical  section  of 
retina  to  show  layers  as  demonstrated  by  the  hjematoxylin-eosin  stain.  (Merkel-Henle.) 
B. — I,  Layer  of  pigmented  epithelium;  2,  layer  of  rods  and  cones;  3,  outer  limiting  layer; 
4,  outer  nuclear  layer;  5,  outer  molecular  layer;  6,  inner  nuclear  layer;  7,  inner  molecular 
layer;  8,  layer  of  nerve  cells;  9,  layer  of  nerve  fibres;  10,  inner  limiting  layer.  A. — i, 
Pigment  layer;  2,  processes  of  pigmented  epithelial  cells  extending  down  between  rods 
and  cones;  3,  rods;  4,  rod-cell  nuclei  and  rod  fibres;  5,  cones;  6,  cone  fibres;  7,  bipolar  cells 
of  inner  nuclear  layer;  8,  ganglion  cells  of  nerve-cell  layer;  9,  larger  ganglion  cells  of  nerve- 
cell  layer;  ID,  fibres  of  optic  nerve  forming  layer  of  nerve  fibres;  11  and  12,  types  of  horizon- 
tal cells;  13,  14,  15,  and  16,  types  of  cells  the  bodies  of  which  lie  in  the  inner  nuclear  layer; 
17,  efferent  optic-nerve  fibre  ending  around  cell  of  inner  nuclear  layer;  iS,  neuroglia  cells; 
19,  Miiller's  fiVjre;  20,  rf)f]-bipf)lar  cell  of  inner  nuclear  layer. 


The  layer  of  rods  and  cones  and  the  outer  nuclear  layer  (Fig.  335, 
B,  2,  4)  are  best  considered  as  subdivisions  of  a  single  layer,  the  neuro- 
epithelial layer.  This  consists  essentially  of  two  forms  of  neuro- 
epithelial elements,  rod  visual  cells  and  cone  visual  cells.  These,  with 
supporting  connective  tissue,  constitute  the  layer  of  rods  and  cones 
and  the  outer  nuclear  layer,  the  separation  into  sub-layers  being  due 


THE  ORGAXS  OF  SPECIAL  SENSE.  503 

to  the  sharp  demarcation  between  the  nucleated  and  non-nucleated 
parts  of  the  cells,  and  the  separation  of  the  two  parts  by  the  perforated 
outer  limiting  membrane. 

The  rod  visual  cell  (Fig.  335,  A,  4)  consists  of  rod,  rod-fibre,  and 
nucleus.  The  rod  (Fig.  335,  A,  3)  is  a  cylinder  from  30  to  40/4  in 
length  and  about  2«  in  diameter.  It  is  divisible  into  an  outer  clear 
portion,  which  contains  the  so-called  "visual  purple"  and  an  inner 
granular  portion.  At  the  outer  end  of  the  latter  is  a  fibrillated  ellip- 
soidal body,  much  more  distinct  in  some  of  the  lower  animals,  the 
ellipsoid  of  Krause.  At  its  inner  end  the  rod  tapers  down  to  a  fine  fibre, 
the  rod  fibre,  which  passes  through  a  perforation  in  the  outer  limiting 
membrane  into  the  outer  nuclear  layer,  where  it  expands  and  contains 
the  nucleus  of  the  rod  visual  cell.  These  nuclei  are  situated  at  various 
levels  in  the  fibre  and  constitute  the  most  conspicuous  element  of  the 
outer  nuclear  layer  (Fig.  t^^^,^,  B,  4). 

The  cone  visual  cell  (Fig.  335,  A,  5,  6)  consists  of  cone,  cone-fibre, 
and  nucleus.  The  cone  (Fig.  t^t,^,  A,  5)  is  shorter  and  broader  than 
the  rod,  and  like  the  latter  is  divisible  into  two  parts.  The  outer  part 
is  short,  clear,  and  tapering,  the  inner  part  broad  and  granular,  and 
like  the  rod  contains  a  fibrillated  ellipsoid  body.  The  cone  fibre 
(Fig.  ;^^^,  A,  6)  is  much  broader  than  the  rod  fibre,  passes  completely 
through  the  outer  nuclear  layer  and  ends  in  an  expansion  at  the  margin 
of  the  outer  molecular  layer.  The  nucleus  of  the  cone  cell  usually  lies 
just  beneath  the  outer  limiting  membrane. 

The  remaining  layers  of  the  retina  must  be  considered  in  relation 
on  the  one  hand  to  the  neuro-epithelium,  on  the  other  to  the  optic 
nerve.  The  inner  nuclear  layer  (Fig.  335,  B,  6)  and  the  layer  of  nerve 
cells  (Fig.  335,  B,  8)  are  composed  largely  of  nerve-cell  bodies,  while  the 
lico  molecular  layers  (Fig.  335,  B,  5,  7)  are  formed  mainly  of  the  rami- 
fications of  the  processes  of  these  cells.  In  the  inner  nuclear  layer 
are  two  kinds  of  nerve  elements,  rod  bipolar  cells  and  cone  bipolar  cells. 
The  bodies  of  these  cells  with  their  large  nuclei  form  the  bulk  of  this 
layer.  From  the  rod  bipolars  (Fig.  335,  A,  20)  processes  (dendrites) 
pass  outward  to  ramify  in  the  outer  molecular  layer  around  the  termi- 
nations of  the  rod  fibres.  From  the  cone  bipolars  (Fig.  335,  .4,  7) 
similar  processes  (dendrites)  extend  into  the  outer  molecular  layer 
where  they  ramify  around  the  terminations  of  the  cone  cells.  Two 
other  forms  of  nerve  cells  occur  in  the  inner  nuclear  layer.  One  is 
known  as  the  horizontal  cell  (Fig.  335,  A,  12).  Its  processes  ramify 
almost  whollv  in  the  outer  molecular  laver.     The  other  lies  alonsf  the 


504  THE  ORGANS. 

inner  margin  of  the  inner  nuclear  layer  and  sends  its  dendrites  into  the 
inner  molecular  layer  (Fig.  335,  A,  13,  14,  15,  and  16).  Many  of  these 
latter  cells  appear  to  have  no  axone  and  are  consequently  known  as 
amacrine  cells. 

The  outer  molecular  layer  is  thus  seen  to  be  formed  mainly  of 
terminations  of  the  rod  and  cone  visual  cells,  of  the  dendrites  of  the 
rod  and  cone  bipolars,  and  of  the  processes  of  the  horizonal  cells. 

From  the  cone  bipolar  a  process  {axone)  extends  inward  to  ramify 
in  the  inner  molecular  layer,  while  from  the  rod  bipolar  a  process 
{axone)  passes  inward  through  the  inner  molecular  layer  to  terminate 
around  the  cells  of  the  nerve-cell  layer. 

The  layer  of  nerve  cells  (Fig.  335,  B,  8)  consists  for  the  most  part 
of  large  ganglion  cells  whose  dendrites  ramify  in  the  inner  molecular 
layer,  and  whose  axones  pass  into  the  layer  of  nerve  fibres  and  thence 
into  the  optic  nerve.  Some  small  ganglion  cells  are  also  found  in  this 
layer,  especially  in  the  region  of  the  macula  lutea  (see  page  505). 

The  inner  molecular  layer  is  thus  seen  to  be  composed  mainly 
of  the  processes  {axones)  of  the  rod  and  cone  bipolars  and  of  the  den- 
drites of  the  ganglion  cells  of  the  nerve-cell  layer. 

The  layer  of  nerve  fibres  (Fig.  335,5,  g)  consists  mainly  of  the  axones 
of  the  just-described  ganglion  cells,  although  a  few  centrifugal  axones 
of  brain  cells  (Fig.  335,  A,  ly)  are  probably  intermingled. 

The  outer  and  inner  limiting  layers  or  membranes  (Fig.  335,  B,  3,  10) 
are  parts  of  the  sustentacular  apparatus  of  the  retina,  being  connected 
with  the  cells  ot  fibres  of  Miiller  (Fig.  335,  A,  19  and  Fig.  336).  The 
latter  form  the  most  conspicuous  elements  of  the  supportive  tissue  of 
the  retina.  They  are  like  the  nerve  elements  proper,  of  ectodermic 
origin  and  are  elongated  cells  which  extend  through  all  the  retinal 
layers,  excepting  the  layer  of  rods  and  cones  and  the  pigment  layer. 
The  inner  ends  of  th-e  cells,  which  are  conical  and  fibrillated,  unite  to 
form  the  inner  limiting  membrane  (Fig.  336,  10).  Through  the  inner 
molecular  layer  the  cell  takes  the  form  of  a  narrow  stalk  with  numerous 
fringe-like  side  fibrils  (Fig  336,  7).  This  widens  in  the  inner  nuclear 
layer,  where  cup-like  depressions  in  the  sides  of  the  Miiller's  cell  are 
caused  by  the  pressure  of  the  surrounding  nerve  cells  (Fig.  336,  b). 
This  wide  portion  of  the  cell  in  the  inner  nuclear  layer  contains  the 
nucleus  (Fig.  336,  a).  In  the  outer  molecular  layer  the  cell  again 
becomes  narrow  (Fig.  336,  5)  and  in  the  outer  nuclear  layer  broadens 
out  into  a  sponge-like  reticulum  (Fig.  336,  4),  which  supports  the  rod 
and  cone  bipolars.     At  the  inner  margin  of  the  layer  of  rods  and 


THE  ORGANS  OF  SPECIAL  SENSE. 


505 


cones  the  protoplasm  of  the  Muller's  cells  spreads  out  and  unites  to 
form  the  so-called  outer  limiting  membrane  (Fig.  336,  3),  from  which 
delicate  fibrils  {fibre  baskets)  pass  outward  between  the  rods  and 
cones.  In  addition  to  the  Muller's  cells,  which  are  neuroglia  ele- 
ments, spider  cells  also  occur  in  the  retina  (Fig.  2>C)S^  -4,  18). 

The  retina  of  the  maeiila  lutea  presents 
certain  peculiarities.  Its  name  is  derived 
from  the  yellow  pigment  which  is  dis- 
tributed diffusely  through  the  inner  layers, 
extending  as  far  out  as  the  outer  molecular 
layer.  The  ganglion-cell  layer  and  the 
inner  nuclear  layer  are  thicker  than  in 
other  parts  of  the  retina .  In  the  layer  of 
rods  and  cones  there  is  a  gradual  reduction 
in  the  number  of  rods,  while  the  number 
of  cones  is  correspondingly  increased. 

In  the  centre  of  the  macula  is  a  de- 
pression, \\\t  fovea  centralis.  As  the  retina 
approaches  this  area  it  becomes  greatly 
thinned,  little  remaining  but  the  layer  of 
cone  cells  and  the  somewhat  thickened 
layer  of  pigmented  epithelium. 

At  the  ora  serrata  the  nervous  elements 
of  the  retina  cease.  The  non-nervous  re 
tinal  extension  over  the  ciliary  body  {pars 
ciliaris  retince)  and  over  the  iris  {pars  iridica 
retmce)  have  been  described  in  connection 
with  the  ciliary  body  and  iris. 

The  Optic  Nerve. — The  optic  nerve 
(Fig.  337,  d)  is  enclosed  by  two  connective- 
tissue  sheaths,  both  of  which  are  extensions 
of  the  brain  membranes.  The  outer  dural 
sheath  (Fig.  337,  a)  is  continuous  with  the 

dura  mater  of  the  brain  posteriorly,  while  anteriorly  it  blends  with 
the  sclera.  The  inner  pial  sheath  (Fig.  337,  &)  is  an  extension  of  the 
pia  mater  and  is  separated  from  the  outer  sheath  by  the  subdural 
space  (Fig.  337,  c).  The  pial  sheath  is  divisible  into  two  sub-layers:  an 
outer  fibrous  layer  (the  so-called  arachnoid),  and  an  inner  vascular  layer. 
These  two  layers  are  separated  by  a  narrow  space,  the  sitbaracJinoid 
space.     The  o|)tic  nerve  fibres,  in  passing  through  the  sclera  and  cho- 


FiG.  336. — Two  Muller's  Fibres 
from  Retina  of  Ox  showing 
Relation  to  Layers  of  Retina. 
(Ramon  y  Cajal.)  3,  Outer 
limiting  layer;  4,  outer  nu- 
clear layer;  5,  outer  molecular 
layer;  6,  inner  nuclear  layer; 
7,  inner  molecular  layer;  8, 
layer  of  nerve  cells;  9,  layer  of 
nerve  fibres;  10,  inner  limiting 
layer;  a,  nucleus;  b,  cup-like 
depression  caused  by  pressure 
from  surrounding  cells. 


506 


THE  ORGANS. 


f    a 


rioid,  separate  the  connective-tissue  bundles  so  that  they  form  a  lattice- 
work, the  already  mentioned  lamina  crihrosa  (Fig.  337,  h).  The  optic 
nerve  fibres  are  medullated,  but  have  no  neurilemma.     Ks  they  pass 

through  the  lamina  cribrosa 
the  medullary  sheaths  are 
lost,  the  fibres  reaching  the 
retina  as  naked  axones. 

Relations  of  Optic 
Nerve  to  Retina  and 
Brain. 

The  rod  and  cone  visual 
cells  are  the  neuro-epi- 
thelial  beginnings  of  the 
visual  tract  (Fig.  335,  A, 
3,  4,  5,  and  6).  By  their 
expanded  bases  in  the  outer 
molecular  layer,  the  rod 
and  cone  cells  communicate 
with  the  neurone  system 
No.  I.  of  the  optic  tract. 
This  comprises  {a)  rod 
neurones,  (&)  cone  neurones, 
(c)  horizontal  neurones. 

Neurone  System  No. 
I. — {a)  Rod  neurones.  The 
cell  bodies  of  these  neurones 
(Fig.  335,  A,  20)  lie  in  the 
inner  nuclear  layer.  Their 
dendrites  enter  the  outer  molecular  layer  where  they  form  networks 
around  the  expanded  bases  of  the  rod  cells.  Their  axones  pass  through 
the  inner  molecular  layer  and  end  in  arborizations  around  the  bodies 
and  dendrites  of  cells  of  the  nerve-cell  layer  (neurone  system  No.  11.) . 
(b)  Cone  neurones  (Fig.  335,  A,  7).  These  have  their  cell  bodies  in  the 
inner  nuclear  layer.  Their  dendrites  ])ass  to  the  outer  molecular 
layer  where  they  form  networks  around  the  expanded  bases  of  the  cone 
cells.  Their  axones  pass  only  into  the  inner  molecular  layer  where 
they  end  in  arborizations  around  the  dendrites  of  neurones  whose  cell 
bodies  are  in  the  layer  of  nerve  cells  (neurone  system  No.  11.) .  (c) 
Horizontal  neurones  (Fig.  335,  ^4,  11  and  12.     These  serve  as  associa- 


FiG.  337. — Section  through  Entrance  of  Optic  Nerve 
into  Eyeball.  (Merkel-Henle.)  a,  Dural  sheath; 
h,  pial  sheath,  inner  and  outer  layers;  c,  space 
between  inner  and  outer  layers  of  pia  mater;  d, 
optic  nerve;  e,  central  artery  of  retina;  a',  sclera; 
/,  chorioid;  g,  retina;  h,  lamina  cribrosa. 


THE  ORGANS  OF  SPECIAL  SENSE. 


507 


tion  neurones  between  the  visual  cells  and  may  be  divided  into  rod 
association  neurones  and  cone  association  neurones.  The  cone  associa- 
tion neurones  are  the  smaller  and  more  superficial  and  both  dendrites 
and  axones  end  in  the  outer  molecular  layer  around  the  terminal  expan- 
sions of  the  cone  visual  cells  (Fig. 
335,  A,  iij.  The  rod  association 
neurones  are  larger,  more  deeply 
seated,  and  behave  in  a  similar 
manner  toward  the  rod  visual  cells 
(Fig.  335,  A,  12).  Some  of  these 
cells  send  processes  to  the  inner 
molecular  layer. 

Neurone  System  No.  II. — 
This  has  been  already  partly  de- 
scribed in  connection  with  the 
axone  terminations  of  neurone 
system  No.  I.  The  cell  bodies  of 
the  second  neurone  system  (Fig. 
335,  A,  8,  9j  are  in  the  layer  of 
nerve  cells  and  are,  as  above  noted, 
associated  either  directly  or  by 
means  of  their  dendrites  with  the 
axones  of  the  first  neurone  system. 
Their  axones  pass  into  the  layer 
of  nerve  fibres  and  ultimately 
become  fibres  of  the  optic  nerve 
(Fig.  335,  .4,  10). 

The  optic  nerves  (Fig.  338,  No) 
unite  at  the  base  of  the  brain  to 
form  the  optic  decussation  or 
chiasma  (Fig.  338,  CM).  Here  the 
axones  from  the  mesial  part  of  the  retina  cross  to  the  optic  tract  of  the 
opposite  side,  while  those  of  the  lateral  part  of  the  retina  remain  in 
the  optic  tract  of  the  same  side.  The  axones  of  the  optic  tract  (Fig. 
338,  Tro)  terminate  in  the  thalamus,  in  the  lateral  geniculate  body,  and 
in  the  anterior  corpus  quadrigeminum  (Fig.  338). 

Neurone  System  No.  III. — The  neurones  of  this  system  have 
their  cell  bodies  in  the  thalamus,  lateral  geniculate  body,  and  anterior 
corpus  cpiadrigeminum  (Fig.  338).  The  axones  of  the  two  former 
terminate  in  the  cortical  visual  centers  in  the  occipital  lobe  (Fig.  ^^^, 


Fig.  338. — Diagram  showing  Main  Rela- 
tions of  Optic  Tract.  (Testut.)  R,  Re- 
tina; Xo,  optic  nerve;  C.V,  optic  decussa- 
tion or  chiasma;  Tro,  optic  tract;  Tho, 
thalamus;  Cgl,  lateral  geniculate  body; 
Qa,  anterior  corpus  quadrigeminum; 
Rd,  fibre  of  optic  tract  passing  directly 
to  cortex;  Sm,  third  neurone  system  of 
optic  tract  (excepting  Rd)  connecting 
thalamus,  lateral  geniculate  body,  and 
anterior  corpus  quadrigeminum  with 
the  cortex,  Co. 


508 


THE  ORGANS. 


Coi-te 


'■\':  ,''","'"V--";--../<r5c.  lonq.boit. 

-Jr.  teeto-bulhtrii  et  sl)ina.LC§ 


:_:  Nu.mN. 


Fig.  zi^- 


THE  ORGANS  OF  SPECIAL  SEXSE.  509 


EXPLANATION  OF  FIG.  339. 

Fig.  339. — Diagram  of  the  Optic  (II)  X^'erve  and  some  of  its  Principal  Connections. 
.4,  Level  of  II  and  III  nerves;  B,  level  of  IV  nerve;  C,  level  of  VI  and  VII  nerves;  D,  spinal 
cord.  The  rods  and  cones  (sensory  cells)  and  the  bipolar  cells  (  =  Neurone  No.  i)  of  the 
retina  are  not  indicated. 

Neurone  No.  2. — 2  a,  Axones  of  ganglion  cells  in  temporal  part  of  retina  pass  to  pul- 
vinar  of  thalamus  of  same  side;  2  b,  axones  of  ganglion  cells  in  retina  pass  to  anterior  corpus 
cjuadrigeminum  of  same  side;  2  c,  axones  of  ganglion  cells  in  retina  pass  to  external  genicu- 
late body  (Corp.  gen.  ext.)  of  same  side;  2  e,  axones  of  ganglion  cells  in  nasal  side  of  retina 
cross  in  optic  chiasma  and  pass  to  external  geniculate  body  of  opposite  side;  2/,  axones  of 
ganglion  cells  in  nasal  side  of  retina  cross  in  optic  chiasma  and  pass  to  anterior  corpus 
quadrigeminum  of  opposite  side;  2  g,  axones  of  ganglion  cells  in  nasal  side  of  retina  cross  in 
optic  chiasma  and  pass  to  pulvinar  of  thalamus  of  opposite  side. 

Neurone  No.  3. — 3  a,  Axones  of  cells  in  pulvinar  to  cortex  of  occipital  lobe  of  cerebrum 
(this  connection  is  disputed);  3  b,  axones  of  cells  in  external  geniculate  body  to  cortex  of 
occipital  lobe  of  cerebrum;  3  a  and  3  b  constitute  the  priman,-  optic  radiation;  3  c,  3  d  and 
3  e,  axones  of  cells  in  middle  layer  of  tectum  (roof)  of  anterior  corpus  quadrigeminum 
decussate  ventral  to  posterior  longitudinal  fasciculus  (dorsal  tegmental  decussation  or 
decussation  of  Meynert)  and  form  the  tractus  tecto-bulbaris  et  spinalis  (Tr.  tecto-bulb. 
et  spin.)  to  bulb  (medulla)  and  anterior  column  of  cord,  innervating  by  collaterals  and 
terminals,  directly  or  indirectly,  chiefly  the  nuclei  of  III,  IV,  VI,  and  VII  cranial  nerves  and 
motor  nuclei  of  spinal  nerves.  3 /and  3  g  (possibly  another  neurone  intercalated  between 
these  and  optic  terminals),  axones  of  cells  in  nucleus  of  posterior  longitudinal  fasciculus 
(Nu.  fasc.  long,  post.)  (X'ucleus  of  Darkschewitsch)  form  part  of  posterior  longitudinal 
fasciculus  and  descend  on  same  side  to  anterior  column  of  cord  next  to  anterior  median 
fissure,  innervating  nuclei  of  III,  IV,  and  VI  cranial  nerves  and  motor  nuclei  of  spinal  nerves. 

Neurmie  No.  4. — Axones  of  cells  in  above-mentioned  motor  nuclei.  Axones  from  cells 
in  median  nucleus  of  III  nerve  (X^u.  med.  Ill  N.),  and  possibly  in  Edinger-Westphal  nu- 
cleus, probably  innervate  the  intrinsic  muscles  of  eyeball  (ciliar)-  and  pupillary  retiex  path). 

It  is  evident  from  the  diagram  that  the  cerebral  pathway  of  the  optic  nerve  is  via  the 
external  geniculate  body  (and  pulvinar  of  thalamus),  and  the  reflex  pathway  is  via  the 
anterior  colliculus  (anterior  corpus  quadrigeminum). 


510 


THE  ORGANS. 


Co).     The  axones  of  the  latter  form  descending  reflex  paths  (see  An- 
terior Corpora  Quadrigemina,  p.  467). 

The  Lens. — The  lens  is  composed  of  lens  fibres  which  are  laid 
down  in  layers  (Fig.  340,  a).  The  lens  fibre  is  a  long  hexagonal, 
flattened  prism  with  serrated  edges.  Most  of  the  lens  fibres  are 
nucleated,  the  nucleus  lying  at  about  the  centre  of  the  fibre  near  the 
axis  of  the  lens.  The  most  central  of  the  lens  libres  are  usually  non- 
nucleated.     The   fibres   extend   meridionally   from   before   backward 

through  the  entire  thickness  of  the 
lens.  They  are  united  by  a  small 
amount  of  cement  substance.  The 
lens  is  surrounded  by  the  lens  capsule 
(Fig.  340,  b),  a  clear  homogeneous 
membrane  which  is  about  i2/«  thick 


Fig.  340. 


Fig.  341. 


Fig.  340. — From  Longitudinal  Section  through  Margin  of  Crystalline  Lens,  showing 
longitudinal  sections  of  lens  fibres  and  transition  from  epithelium  of  capsule  into  lens  fibres. 
(Merkel-Henle.)     a,  Lens  fibres;  b,  capsule;  c,  epithelium. 

Fig.  341. — From  Cross  Section  of  Crystalline  Lens,  showing  transverse  sections  of  lens 
fibres  and  surface  epithelium.     (Merkel-Henle.)     a,  Lens  fibres;  b,  epithelium. 


over  the  anterior  surface  of  the  lens,  about  half  as  thick  over  the 
posterior  surface.'  Between  the  capsule  and  the  anterior  and  lateral 
surfaces  of  the  lens  is  a  single  layer  of  cuboidal  epithelial  cells  (Fig. 
340,  c),  the  lens  epithelium.  Attached  to  the  capsule  of  the  lens  an- 
teriorly and  posteriorly  are  membrane-like  structures  which  constitute 
the  suspensory  ligament  of  the  lens.  These  pass  outward  and  unite  to 
form  a  delicate  memljrane,  the  zonula  ciliaris  or  zonule  of  Zinn  (Fig. 
333).     This  bridges  over  the  incc|ualities  of  the  ciliary  ])rocesses  and. 


THE  ORGANS  OF  SPECIAL  SENSE.  511 

continuing  as  the  hyaloid  membrane,  forms  a  Hning  for  the  vitreous 
cavity  of  the  eye.  The  triangular  space  between  the  two  layers  of  the 
suspensory  ligament  and  the  lens  is  known  as  the  canal  of  Petit. 

The  vitreous  body  is  a  semifluid  substance  containing  fibres  which 
run  in  all  directions  and  a  small  number  of  connective-tissue  cells 
and  leucocytes.  Traversing  the  vitreous  in  an  antero-posterior  direc- 
tion is  the  so-called  hyaloid  or  Cloquet''s  canal,  the  remains  of  the  em- 
bryonic hyaloid  artery  (page  516). 

Blood-vessels. — The  blood-vessels  of  the  eyeball  are  divisible 
into  two  groups,  one  group  being  branches  of  the  central  artery  of  the 
retina,  the  other  being  branches  of  the  ciliary  artery. 

The  central  artery  of  the  retina  enters  the  eyeball  through  the  cen- 
tre of  the  optic  nerve.  Within  the  eyeball  it  divides  into  two  branches, 
a  superior  and  an  inferior.  These  pass  anteriorly  in  the  nerve-fibre 
layer,  giving  off  branches,  which  in  turn  give  rise  to  capillaries  which 
supply  the  retina,  passing  outward  as  far  as  the  neuro-epithelial  layer 
and  anteriorly  as  far  as  the  ora  serrata.  The  smaller  branches  of  the 
retinal  arteries  do  not  anastomose.  In  the  embryo  a  third  vessel  exists, 
the  hyaloid  artery.  This  is  a  branch  of  the  central  retinal  artery  and 
traverses  the  vitreous  to  the  posterior  surface  of  the  lens,  supplying  these 
structures.  The  hyaloid  canal,  or  canal  of  Cloquet,  of  the  adult 
vitreous,  represents  the  remains  of  the  degenerate  hyaloid  artery  (page 
516).     The  veins  of  the  retina  accompany  the  arteries. 

The  ciliary  arteries  are  divisible  into  long  ciliary  arteries,  short 
ciliary  arteries,  and  anterior  ciliary  arteries.  The  long  ciliary  arte- 
ries are  two  in  number  and  pass  one  on  each  side  between  the  cho- 
rioid  and  sclera  to  the  ciliary  body,  where  each  divides  into  two 
branches,  which  diverge  and  run  along  the  ciliary  margin  of  the  iris. 
Here  the  anastomosis  of  the  two  long  ciliary  arteries  forms  the  greater 
arterial  circle  of  the  iris.  This  gives  rise  to  small  branches  which  pass 
inward  supplying  the  surrounding  tissues  and  unite  near  the  margin 
of  the  pupil  to  form  the  lesser  arterial  circle  of  the  iris.  The  branches 
of  the  short  ciliary  arteries  pierce  the  sclera  near  the  optic  nerve  entrance, 
supply  the  posterior  part  of  the  sclera,  and  terminate  in  the  chorio- 
capillaris  of  the  chorioid.  The  anterior  ciliary  arteries  enter  the 
sclera  near  the  corneal  margin  and  communicate  with  the  chorio- 
capillaris  and  with  the  greater  arterial  circle  of  the  iris.  The  anterior 
ciliary  arteries  also  supply  the  ciliary  and  recti  muscles  and  partly 
supply  the  sclera  and  conjuncti\"a.  Small  ^■ei^s  accompany  the  ciliary 
arteries;  the  larger  veins  of  this  area  are  i^eculiar,  howc\cr,  in  that 


512  THE  ORGANS. 

they  do  not  accompany  the  arteries,  but  as  venae  vorticosae  converge 
toward  four  centres,  one  in  each  quadrant  of  the  eyeball.  At  the 
sclero-corneal  junction  is  a  venous  channel,  the  canal  of  Schlemm, 
which  completely  encircles  the  cornea  (Fig.  ;^S3)- 

Lymphatics. — The  eyeball  has  no  distinct  lymph-vessel  system. 
The  lymph,  however,  follows  certain  definite  directions  which  have 
been  designated  by  Schwalbe  "lymph  paths."  He  divides  them 
into  anterior  lymph  paths  and  posterior  lymph  paths.  The  anterior 
lymph  paths  comprise  (a)  the  anterior  chamber  which  communicates 
by  means  of  a  narrow  cleft  between  iris  and  lens  with  the  posterior 
chamber;  (b)  the  posterior  chamber;  (c)  the  lymph  canaliculi  of  the 
sclera  and  cornea  and  the  canal  of  Petit.  The  posterior  lymph  paths 
include  {a)  the  hyaloid  canal  (see  above);  (b)  the  subdural  and  in- 
tra-pial  spaces,  including  the  capsule  of  Tenon;  (c)  the  perichorioidal 
space,  and  {d)  the  perivascular  and  pericellular  lymph  spaces  of  the 
retina. 

Nerves. — The  nerves  which  supply  the  eyeball  pass  through  the 
sclera  with  the  optic  nerve  and  around  the  eyeball  in  the  supra- 
chorioid  layer.     From  these  nerves,  branches  are  given  off  as  follows: 

(t)  To  the  chorioid,  where  they  are  intermingled  with  ganglion 
cells. 

(2)  To  the  ciliary  body,  where  they  are  mingled  with  ganglion  cells 
to  form  the  ciliary  plexus.  The  latter  gives  off  branches  to  the  ciliary 
body  itself,  to  the  iris,  and  to  the  cornea.  Those  to  the  cornea  first 
form  a  plexus  in  the  sclera — the  plexus  annularis — which  encircles  the 
cornea.  From  this,  branches  pierce  the  substantia  propria  of  the 
cornea,  where  they  form  four  corneal  plexuses,  one  in  the  posterior 
part  of  the  substantia  propria,  a  second  just  beneath  the  anterior  elastic 
membrane,  a  third  sub-epithelial,  and  a  fourth  intra-epithelial.  The 
fibres  of  the  last  named  are  extremely  delicate  and  terminate  freely 
between  the  epithelial  cells.  Krause  describes  end-bulbs  as  occurring 
in  the  substantia  propria  near  the  margin  of  the  sclera,  while  according 
to  Dogicl  some  of  the  fibres  are  connected  with  end-plates. 

The  Lacrymal  Apparatus. 

The  lacrymal  ajjparatus  of  each  eye  consists  of  the  gland,  its  excre- 
tory ducts,  the  lacrymal  canal,  the  lacrymal  sac,  and  the  nasal  duct. 

The  lacrymal  gland  is  a  com])Ound  tubular  gland  consisting  of 
two  main  lobes.     Its  structure  corresponds  in  general  to  that  of  a 


THE  ORGANS  OF  SPECIAL  SExXSE.  513 

serous  gland.  The  excretory  ducts  are  lined  with  a  two-layered  col- 
umnar epithelium  which  becomes  simple  columnar  in  the  smaller  ducts. 
The  alveoli  are  lined  with  irregularly  cuboidal  serous  cells,  which  rest 
upon  a  basement  membrane  beneath  which  is  a  richly  elastic  interstitial 
tissue. 

The  lacrymal  canals  have  a  stratified  squamous  epithelial  lining. 
This  rests  upon  a  basement  membrane  beneath  which  is  the  stroma 
containing  many  elastic  fibres.  External  to  the  connective  tissue  are 
some  longitudinal  muscle  fibres. 

The  lacrymal  sac  is  lined  with  a  two-layered  stratified  or  pseudo- 
stratified  columnar  epithelium  resting  upon  a  basement  membrane. 
The  stroma  contains  much  diffuse  lymphatic  tissue. 

The  nasal  duct  has  walls  similar  in  structure  to  those  of  the  lacrymal 
sac.  In  the  case  of  both  sac  and  duct  the  walls  abut  against  perios- 
teum, a  dense  vascular  plexus  being  interposed. 

The  blood-vessels,  lymphatics,  and  nerves  of  the  lacrymal  gland 
have  a  distribution  similar  to  those  of  other  serous  glands. 

The  Eyelid. 

The  eyelid  consists  of  an  outer  skin  layer,  an  inner  conjunctival 
layer,  and  a  middle  connective-tissue  layer. 

The  epidermis  is  thin  and  the  papillae  of  the  derma  are  low.  Small 
sebaceous  glands,  sweat  glands,  and  fine  hairs  are  present. 

The  conjunctiva  (Fig.  342,  d)  is  a  mucous  membrane  consisting 
of  a  lining  epithelium  and  a  stroma.  The  epithelium  is  stratified 
columnar  consisting  of  two  or  three  layers  of  cells.  Among  these 
cells  are  cells  resembling  goblet  cells.  Although  not  always  upon 
the  surface,  they  are  believed  to  be  mucous  cells,  probably  analogous 
to  the  so-called  Leydig's  cells  found  in  the  larvae  of  amphibians  and 
fishes.  Dift'use  lymphoid  tissue  is  regularly  present  in  the  stroma, 
while  lymph  nodules  are  of  rare  occurrence.  Small  glands,  similar 
to  the  lacrymal  glands  in  structure,  are  usually  present  (Fig.  342,  k). 

At  the  margin  of  the  eyelid  where  skin  joins  mucous  membrane 
are  several  rows  of  large  hairs,  the  eyelashes  (Fig.  342,  h).  Connected 
with  their  follicles  are  the  usual  sebaceous  glands  (Fig.  342,  g)  and  the 
glands  of  Mall,  the  latter  probably  representing  modified  sweat  glands. 

The  middle  layer  contains  the  tarsus  (Fig.  342,  c)  and  the  mus- 
cular structure  of  the  eyelid  (Fig.  342,  b).  The  tarsus  is  a  plate  of 
dense  fibrous  tissue  which  lies  iust  beneath  the  coniuncli\'a  and  ex- 


514 


THE  ORGANS. 


tends  about  two-thirds  the  height  of  the  Hd.  It  contains  the  tarsal 
or  Meibomian  glands  (Fig.  342,  e).  These  are  from  thirty  to  forty 
in  number,  each  consisting  of  a  long  duct  which  opens  externally  on 

c  the   margin   of  the  lid  behind 

the  lashes  (Fig.  342,  /),  and 
internally  into  a  number  of 
branched  tubules.  The  duct  is 
lined  with  stratified  squamous 
epithelium.  The  tubules  re- 
semble those  of  the  sebaceous 
glands.  Between  the  tarsus 
and  the  skin  are  the  muscular 
structures  of  the  eyehd  in  which 
both  smooth  and  striated  mus- 
cle are  found. 

Blood-vessels. — Two  main 
arteries  pass  to  the  eyelid,  one 
at  each  angle  and  unite  to  form 
an  arch,  the  tarsal  arch,  along 
the  margin  of  the  lid.  A  second 
arch,  the  external  tarsal  arch, 
is  formed  along  the  upper 
margin  of  the  tarsus.  From 
these  arches  are  given  off  capil- 
lary networks  which  supply  the 
structures  of  the  lid. 

Lymphatics. — These  form 
two  anastomosing  plexuses,  one 
anterior,  the  other  posterior  to 
the  tarsus. 

Nerves. — The  nerves  form 
plexuses  in  the  substance  of  the 
lid.       From     these,     terminal 
fibrils  pass  to  the  various  struc- 
tures of  the  lid.      Many  of  the 
fibres   end   freely   in   fine   net- 
works around  the  tarsal  glands,  u]jon   the  blood-vessels,   and  in  the 
epithelium  of  the  conjunctiva.      Other  fibres  terminate  in  end-bulbs 
which  arc  especially  numerous  at  the  margin  of  the  lid. 


Fig.  342. — Vertical  Section  througli  Upper 
Eyelid.  (Waldeyer.)  a,  Skin;  h,  orbicularis 
mu.scle;  b',  ciliary  bundle  of  muscle;  c,  in- 
voluntary muscle  of  eyelid;  d,  conjunctiva; 
e,  tarsus  containing  Meibomian  glands;  /, 
duct  of  Meibomian  gland;  g,  sebaceous 
gland  with  duct  lying  near  eyelashes;  h, 
eyelashes;  i,  small  hairs  in  outer  skin;  j, 
sweat  glands;  k,  yjosterior  tarsal  glands. 


THE  OROAXS  OF  SPECIAL  SENSE. 

Development  of  the  Eye. 


.3L5 


The   eyes  begin   their  development  very  early  in   embryonic   life. 
As  optic  depressions  they  are  visible  even  before  the  closure  of  the  med- 


Fore-brain  vesicle 


Lens  area 


Ootic  vesicle    ' 


Surface  ectoderm 


Optic  vesicle 


Fig.  343. — Section  through  head  of  chick  of  two  days'  incubation.  (Duval.)  The 
formation  of  the  optic  vesicle  and  stalk  appears  to  be  somewhat  more  advanced  on  tlie 
left  than  on  the  right. 


ullary  groove.  As  a  result  of  the  closure  of  this  groove,  the  optic 
depressions  are  transformed  into  the  optic  vesicles.  The  connection 
between  vesicle  and  brain  now^  becomes  narrowed  so  that  the  two  are 


Fore-brain 


Lens  invagination  - 


Optic  vesicle 


-  Lens  invagination 


Optic  vesicle 
Fig.   344. — Section  through  head  of  chick  of  three  days'  incubation.      (I)u\-al.) 


connected  only  by  the  thin  optic  stalk.  The  surface  of  the  optic  \"esicle 
Ijccomes  tirmly  adherent  to  the  e])idermis  and  as  a  result  of  ]irolifera- 
tion  of  ectodermic  cells  at  this  ])oint  is  |)ushed  inward  (in\'aginated). 


516 


THE  ORGANS. 


forming  the  optic  cup.  The  invagination  of  the  optic  vesicle  extends 
also  to  the  stalk,  the  sulcus  in  the  latter  being  known  as  the  chorioid 
fissure.     The  latter  serves  for  the  introduction  of  mesenchyme,  and 


Fore-brain  —  — -M 


Lens  vesicle  - 


Optic  cup- 


Fig.  345. — Showing  somewhat  later  stage  in  development  of  optic  cup  and  lens 
than  is  shown  in  Fig.  344.     (Duval.) 


the  development  of  the  hyaloid  retinal  artery.  Three  distinct  parts 
may  now  be  distinguished  in  the  developing  eye,  which  at  this  stage 
is  known  as  the  secondary  optic  vesicle:  {a)  The  proliferating  epidermis 


Conjunctival  epithelium 7 


Vitreous 


Lens  vesicle  -  ■ 


Retina  (inner  layer . 
of  optic  cup) 


Pigmented  layer  of  retina 
(outer  layer  of  optic  cup) ' 


Optic  stalk 


Fig.  346.— Diagram  oi  developing  lens  and  optic  cup.  (Duval.)  The  cells  of  the 
inner  wall  of  the  lens  vesicle  have  begun  to  elongate  to  form  lens  fibers.  The  epithelium 
over  the  lens  is  the  aniage  of  the  corneal  epithelium.  The  mosodermal  tissue  between 
the  latter  and  the  anterior  wall  of  the  lens  vesicle  is  the  aniage  of  the  substancia  propria 
corner. 


which  is  to  form  the  lens;  (b)  the  more  superficial  of  the  in\-aginated 
layers  which  is  to  become  the  retina;  and  (c)  the  surrounding  meso- 
dermic  tissue  from  which  the  outer  coats  of  the  eye  are  to  develop. 


THE  ORGANS  OF  SPCEIAL  SENSE.  51' 


TECHNIC. 


(i)For  the  study  of  the  general  structures  of  the  eyeball  the  eye  of  some  large 
animal,  such  as  an  ox,  is  most  suitable.  Fix  the  eye  for  about  a  week  in  ten-per- 
cent, formalin.  Then  wash  in  water  and  bisect  the  eye  in  such  a  manner  that  the 
knife  passes  through  the  optic-nerve  entrance  and  the  centre  of  the  cornea.  The 
half  eye  should  now  be  placed  in  a  dish  of  water  and  the  structures  shown  in  Fig. 
328  identified  with  the  naked  eye  or  dissecting  lens.  On  removing  the  vitreous 
and  retina,  the  pigmented  epithelium  of  the  latter  usually  remains  attached  to  the 
chorioid  from  which  it  may  be  scraped  and  examined  in  water  or  mounted  in  gly- 
cerin. In  removing  the  lens  note  the  lens  capsule  and  the  suspensory  ligament. 
The  lens  may  be  picked  to  pieces  with  the  forceps,  and  a  small  piece,  after  further 
teasing  with  needles,  examined  in  water  or  mounted  in  glycerin  or  eosin-glycerin. 
The  retinal  surface  of  the  chorioid  shows  the  iridescent  membrane  of  Bruch.  By 
placing  a  piece  of  the  chorioid,  membrane-of-Bruch-side  down,  over  the  tip  of  the 
finger  and  gently  scraping  with  a  knife  in  the  direction  of  the  larger  vessels,  the 
latter  may  be  distinctly  seen.  By  now  staining  the  piece  lightly  with  haematoxylin 
and  strongly  with  eosin,  clearing  in  oil  or  origanum  and  mounting  in  balsam,  the 
choriocapillaris  and  the  layer  of  straight  vessels  become  distinctly  visible  with 
the  low-power  lens.  In  removing  the  chorioid  note  the  close  attachment  of  the 
latter  to  the  sclera,  this  being  due  to  the  intimate  association  of  the  fibres  of  the 
lamina  suprachorioidea  and  of  the  lamina  fusca.  If  the  brown  shreds  attached  to 
the  inner  side  of  the  sclera  be  examined,  the  pigmented  connective-tissue  cells  of 
the  sclera  can  be  seen. 

(2)  For  the  study  of  the  finer  structure  of  the  coats  of  the  eye,  a  human  eye  if 
it  is  possible  to  obtain  one,  if  not,  an  eye  from  one  of  the  lower  animals,  should 
be  fixed  in  formalin-Muller's  fluid  (technic  5,  p.  7)  and  hardened  in  alcohol.  (A 
few  drops  of  strong  formalin  injected  by  means  of  a  hypodermic  needle  directly 
into  the  vitreous  often  improves  the  fixation.)  The  eye  should  next  be  divided 
into  quadrants  by  first  carrying  the  knife  through  the  middle  of  the  cornea  and  of 
the  optic-nerve  entrance  and  then  dividing  each  half  into  an  anterior  and  a  poste- 
rior half.  Block  in  celloidin,  cut  the  following  sections,  and  stain  with  hitmatoxy- 
lin-eosin  (technic  i,  p.  18). 

(a)  Section  through  the  sclero-corneal  junction,  including  the  ora  serrata, 
ciliary  body,  iris,  and  lens.  Before  attempting  to  cut  this  section  almost  all  of  the 
lens  should  be  picked  out  of  the  block,  leaving  only  a  thin  anterior  and  lateral  rim 
attached  to  the  capsule  and  suspensory  ligament.  The  block  should  then  be  so 
clamped  to  the  microtome  that  the  lens  is  the  last  part  of  the  block  to  be  cut.  The 
above  precautions  are  necessary  on  account  of  the  density  of  the  lens,  making  it 
difficult  to  cut. 

(b)  Section  through  the  postero-lateral  portion  of  the  eyeball  to  show  struc- 
ture of  sclera,  chorioid,  and  retina.  This  section  should  be  as  thin  as  possible  and 
perpendicular  to  the  surface. 

(c)  Section  through  the  entrance  of  the  ojnic  nerve.  Ha^matoxylin-picro-acid- 
fuchsin  also  makes  a  good  stain  for  this  section.  It  is  instructive  in  cutting  the 
eye  to  cut  a  small  segment  from  the  optic  nerve  and  to  block  it  with  the  optic- 
nerve  entrance  material  in  such  a  manner  that  it  is  cut  transvenselv.     In  this  wav 


,518  THE  ORGANS. 

both  longitudinal  and  transverse  sections  of  the  optic  nerve  appear  in  the  same 
section. 

(d)  For  the  study  of  the  neurone  relations  of  the  retina  material  must  be 
treated  by  one  of  the  Golgi  methods  (page  32). 

(4)  The  connective-tissue  cells  and  cell  spaces  of  the  cornea  may  be  demon- 
strated by  means  of  technics  8  and  9,  page  81. 

(5)  The  different  parts  of  the  lacrymal  apparatus  may  be  studied  by  fixing 
material  in  formalin-MuUer's  fluid  and  staining  sections  in  hasmatoxylin-eosin. 

(6)  The  Eyelid.  An  upper  eyelid,  human  if  possible,  should  be  carefully 
pinned  out  on  cork,  skin  side  down,  and  fixed  in  formalin-Miiller's  fluid.  Vertical 
sections  should  be  stained  with  haematoxylin-eosin  or  with  hcematoxylin-picro-acid- 
fuchsin. 

The  Organ  of  Hearing. 

The  organ  of  hearing  comprises  the  external  ear,  the  middle  ear, 
and  the  internal  ear. 

The  External  Ear. 

The  external  ear  consists  of  the  pinna  or  auricle,  the  external 
auditory  canal,  and  the  outer  surface  of  the  tympanic  membrane. 

The  pinna  consists  of  a  framework  of  elastic  cartilage  embedded  in 
connective  tissue  and  covered  by  skin.  The  latter  is  thin  and  con- 
tains hairs,  sebaceous  glands,  and  sweat  glands. 

The  external  auditory  canal  consists  of  an  outer  cartilaginous  por- 
tion and  an  inner  bony  portion.  Both  are  lined  with  skin  continuous 
with  that  of  the  surface  of  the  pinna.  In  the  cartilaginous  portion  of 
the  canal  the  skin  is  thick  and  the  papillae  are  small.  Hair,  sebaceous 
glands,  and  large  coiled  glands  (ceruminous  glands)  are  present.  The 
last  named  resemble  the  glands  of  Mall  (page  513)  and  are  probably 
modified  sweat  glands.  Their  cells  contain  numerous  fat  droplets 
and  pigment  granules.  They  have  long  narrow  ducts  lined  with  a 
two-layered  epithelium.  In  children  these  ducts  open  into  the  hair 
follicles;  in  the  adult  they  o|)en  on  the  surface  near  the  hair  follicles. 
'I"he  secretion  of  these  glands  ])lus  des(juamated  e])ithelium  consti- 
tutes the  ear  wax.  In  the  bony  portion  of  the  canal  the  skin  is  thin, 
free  from  glands  and  hair,  and  firmly  adherent  to  the  periosteum. 

'j'he  tympanic  membrane  (ear  drum)  separates  the  external  ear 
from  the  middle  ear.  It  consists  of  three  layers:  a  middle  layer  or 
substantia  propria,  an  outer  layer  continuous  with  the  skin  of  the  ex- 
ternal ear,  and  an  inner  layer  continuous  with  the  mucous  mem- 
brane of  the  middle  ear. 


THE  ORGANS  OF  SPECIAL  SEXSE.  .519 

The  substantia  propria  consists  of  closely  wo\'en  connective-tis- 
sue fibres,  the  outer  fibres  having  a  radial  direction  from  the  head  of 
the  malleus,  the  inner  fibres  having  a  concentric  arrangement  and 
being  best  developed  near  the  periphery. 

The  outer  layer  of  the  tympanic  membrane  is  skin,  consisting  of 
epidermis  and  of  a  thin  non-papillated  corium,  excepting  over  the 
manubrium  of  the  malleus,  where  the  skin  is  thicker  and  pajjillated. 

The  inner  layer  is  mucous  membrane  and  consists  of  a  stroma  of 
fibro-elastic  tissue  covered  with  a  single  layer  of  low  epithelial  cells. 

Blood-vessels. — Blood  is  supplied  to  the  tympanic  membrane  by 
two  sets  of  vessels,  an  external  set  derived  from  the  vessels  of  the 
external  auditory  meatus  and  an  internal  set  from  the  vessels  of  the 
middle  ear.  These  give  rise  to  capillary  networks  in  the  skin  and 
mucous  membrane,  respectively,  and  anastomose  by  means  of  perfo- 
rating branches  at  the  periphery  of  the  membrane.  From  the  capil- 
laries the  blood  passes  into  two  sets  of  small  veins,  one  extending  around 
the  periphery  of  the  membrane,  the  other  following  the  handle  of  the 
malleus. 

Lymphatics. — These  follow  in  general  the  course  of  the  blood- 
vessels.    They  are  most  numerous  in  the  outer  layer. 

Nerves. — The  larger  nerves  run  in  the  substantia  propria.  From 
these,  branches  pass  to  the  skin  and  mucous  membrane,  beneath  the 
surfaces  of  which  they  form  plexuses  of  fine  fibres. 

The  Middle  Ear. 

The  middle  ear  or  tympanum  is  a  small  chamber  separated  from 
the  external  ear  by  the  tympanic  membrane  and  communicating  with 
the  ]>harynx  by  means  of  the  Eustachian  tube.  Its  walls  arc  formed 
by  the  surrounding  bony  structures  covered  by  periosteum.  It  is 
lined  with  mucous  membrane  and  contains  the  ear  ossicles  and  their 
ligamentous  and  muscular  attachments.  The  epithelium  is  of  the 
simple  low  cuboidal  type.  In  places  it  may  be  ciliated  and  not  infre- 
quently assumes  a  pseudostratified  character  with  two  layers  of  nuclei. 
Beneath  the  epithelium  is  a  thin  stroma  which  contains  some  ditluse 
lymphoid  tissue  and  blends  with  the  dense  underlying  ])cri()stcum. 
Small  tubular  glands  are  usually  present,  es])ecially  near  the  ojiening  of 
the  Eustachian  tul)e. 

The  fenestra  rotunda  is  covered  l)y  the  secondary  tympanic  irem- 
brane.     This  consists  of  a  central  lamina  of  connecti\"e  tissue  coxcred 


520 


THE  ORGANS. 


on  its  tympanic  side  by  part  of  the  mucous  membrane  of  that  cham- 
ber, on  the  opposite  side  by  a  single  layer  of  endothelium. 

The  ossicles  are  composed  of  bone  tissue  arranged  in  the  usual 
systems  of  lamellae.  The  stapes  alone  contains  a  marrow  cavity.  Over 
their  articular  surfaces  the  ossicles  are  covered  by  hyaline  cartilage. 

The  Eustachian  Tube. — This  is  a  partly  bony,  partly  cartilaginous 
canal  lined  with  mucous  membrane.  The  epithelium  of  the  latter  is 
of  the  stratified  columnar  ciliated  variety  consisting  of  two  layers  of 
cells.  In  the  bony  portion  of  the  tube  the  stroma  is  small  in  amount 
and  intimately  connected  with  the  periosteum.  In  the  cartilaginous 
portion  the  stroma  is  thicker  and  contains,  especially  near  the  pharyn- 
geal opening,  lymphoid  tissue  and  simple  tubular  mucous  glands. 


Ampunac 


The  Internal  Ear. 

The  internal  ear  consists  of  a  complex  series  of  connected  bony 
walled  chambers  and  passages  containing  a  similar-shaped  series  of 
membranous  sacs  and  tubules.  These  are  known,  respectively,  as  the 
osseous  labyrinth  and  the  membranous  labyrinth.     Between  the  two  is  a 

lymph  space,  which  contains  the 
so-called  perilymph,  while  within 
the  membranous  labyrinth  is  a 
similar  fluid,  the  endolymph. 

The  bony  labyrinth  consists 
of  a  central  chamber,  the  vesti- 
bule, from  which  are  given  off 
the  three  semicircular  canals  and 
the  cochlea.  The  vestibule  is 
separated  from  the  middle  ear 
by  a  plate  of  bone  in  which  are 
two  openings,  the  fenestra  ovalis 
and  the  fenestra  rotunda.  Just 
after  leaving  the  vestibule  each  canal  presents  a  dilatation,  the 
ampulla.  As  each  canal  has  a  return  opening  into  the  vestibule  and  as 
the  anterior  and  posterior  canals  have  a  common  return  opening  (the 
canalis  communis),  there  are  five  openings  from  the  vestibule  into  the 
semicircular  canals  (Fig.  347).  The  bony  labyrinth  is  lined  with 
periosteum,  covered  by  a  single  layer  of  endothelial  cells. 

The  Vestibule  and  the  Semicircular  Canals. — In  the  vestibule 
the  membranous  labyrinth  is  subdivided  into  two  chambers,  the  sac- 


Amjjidla 


Fig.  347. — The  Bony  Labyrinth 
mann.) 


X3.  (Heitz- 


THE  ORGANS  OF  SPECIAL  SENSE. 


521 


cule  and -the  utricle,  which  are  connected  by  the  iitriculo-sacciilar  duct. 
From  the  latter  is  given  off  the  endolymphatic  c/z^c/ which  communicates, 
through  the  aqueduct  of  the  vestibule,  with  a  subdural  lymph  space, 
the  endolymphatic  sac.  The  saccule  opens  by  means  of  the  ductus 
reuniens  into  the  cochlea,  while  the  utricle  opens  into  the  ampullae  of 
the  semicircular  canals.  The  saccule  and  utricle  only  partly  fill  the 
vestibule,  the  remaining  space,  crossed  by  fibrous  bands  and  lined  with 
endothelium,  constituting  the  perilymphatic  space. 


Fig.  34S. — Diagram  of  the  Perilymphatic  and  Endolymphatic  Spaces  of  the  Inner  Ear. 
(Testut.)  Endolymphatic  spaces  in  gray;  perilymphatic  spaces  in  black,  i,  Utricle;  2,  sac- 
cule; 3,  semicircular  canals;  4,  cochlear  canal;  5,  endolymphatic  duct;  h,  subdural  endo- 
lymphatic sac;  7,  canalis  reuniens;  8,  scala  tympani;  g,  scala  vestibuli;  10,  their  union  at 
the  helicotrema;  11,  aqueduct  of  the  vestibule;  12,  aqueduct  of  the  cochlea;  13,  perios- 
teum; 14,  dura  mater;  15,  stapes  in  fenestra  ovalis;  16,  fenestra  rotunda  and  secondary 
tympanic  membrane. 

Saccule  and  Utricle. — The  walls  of  the  saccule  and  of  the  utricle 
consist  of  fine  fibro-elastic  tissue  supporting  a  thin  basement  membrane, 
upon  which  rests  a  single  layer  of  low  epithelial  cells.  In  the  wall  of 
each  chamber  is  an  area  of  special  nerve  distribution,  the  macula 
acustica.  Here  the  epithelium  changes  to  high  columnar  and  consists 
of  two  kinds  of  cells,  sustentacular  and  neuro-epithelial.  The  sustentac- 
ular  cells  are  long,  irregular,  nucleated  cylinders,  narrow  in  the  middle, 
widened  at  each  end,  the  outer  end  being  frecpiently  split  and  resting 
upon  the  l^asement  membrane.  The  ncuro-cpitJiclial  cells  or  "hair 
cells"  arc  short  cvlindcrs  which  extend  onlv  about  halfwav  ihrouEfh 


.522  THE  ORGANS. 

the  epithelium.  The  basal  end  of  the  cell  is  the  larger  and  contains 
the  oval  nucleus.  The  surface  of  the  cell  is  provided  with  a  cuticular 
margin  from  which  project  several  long  hair-like  processes,  the  auditory 
hairs.  Small  crystals  of  calcium  carbonate  are  found  on  the  surfaces 
of  the  hair  cells.  These  are  known  as  otoliths  and  are  embedded  in  a 
soft  substance,  the  otolithic  membrane.  The  hair  cells  are  the  neuro- 
epithelial end-organs  of  the  vestibular  division  of  the  auditory  nerve 
and  are,  therefore,  closely  associated  with  the  nerve  fibres.     The  latter 


Fig.  34Q. — Diagram  of  the  Right  Membranous  Labyrinth.  (Testut.)  i,  Utricle;  2 
superior  semicircular  canal;  3,  posterior  semicircular  canal;  4,  external  semicircular  canal;  5, 
saccule;  6,  endolymphatic  duct;  7  and  7',  canals  connecting  utricle  and  saccule  respectively 
with  the  endolymphatic  duct;  8,  endolymphatic  sac;  9,  cochlear  duct;  9',  its  vestibular 
cul-de-sac;  9",  its  terminal  cul-de-sac;  10,  canalis  reuniens. 

on  piercing  the  basement  membrane  lose  their  medullary  sheaths  and 
split  up  into  several  small  branches,  which  form  a  horizontal  plexus 
between  the  basement  membrane  and  the  bases  of  the  hair  cells.  From 
this  plexus  are  given  off  fibrils  which  end  freely  l^etween  the  hair  cells. 

Semicircular  Canals. — The  walls  of  the  semicircular  canals  are 
similar  in  structure  to  the  walls  of  the  saccule  and  utricle;  they  also 
bear  a  similar  relation  to  the  walls  of  the  bony  canal.  Along  the 
concavity  of  each  canal  the  e]Mthelium  is  somewhat  higher,  forming 
the  raphe.  In  each  ampulla  is  a  crista  acustica,  the  structure  of 
which  is  similar  to  that  of  the  maculae  of  the  saccule  and  utricle. 
With  the  adjoining  high  columnar  cells,  this  forms  the  so-called 
semilunar  fold.  As  in  the  case  of  the  maculae  the  hair  cells  have  otoliths 
upon  their  surfaces,  the  otolithic  membrane  here  forming  a  sort  of 
dome  over  the  hair  cells  known  as  the  cupula. 

The  Cochlea.  The  bony  cochlea  consists  of  a  conical  axis,  the 
modiolus,  around  which   winds  a  spiral  Ijony  canal.     This  canal  in 


THE  ORGANS  OF  SPECIAL  SENSE. 


.523 


man  makes  about  two  and  one-half  turns,  ending  at  the  rounded  tip 
of  the  cochlea  or  cupola.  Projecting  from  the  modiolus  partly  across 
the  bony  canal  of  the  cochlea  is  a  plate  of  bone,  the  bony  spiral  Uuuiiia 
(Fig.  351,  x).  This  follows  the  spiral  turns  of  the  cochlea,  ending  at 
the  cupola  in  a  hook-shaped  process,  the  hamulus.  Along  the  outer 
side  of  the  canal,  opposite  the  bony  spiral  lamina,  is  a  projection  of 
thickened  periosteum,  the  spiral  ligament  (Fig.  351,  h).  A  connective- 
tissue  membrane,  the  membranous  spiral  lamina  (Fig.  351,  5),  crosses 


Fig.  350. — The  Membranous  Labyrinth  from  the  Right  Internal  Ear  of  a  Human 
Embryo  at  the  Fifth  Month;  seen  from  the  Medial  Side.  (After  Retzius,  from  Barker.) 
1-5,  Utricle;  2,  utricular  recess;  3,  macula  acustica  of  utricle;  4,  posterior  sinus;  5,  superior 
sinus;  6,  7,  8,  superior,  lateral,  and  posterior  ampullfe;  g,  10,  11,  superior,  posterior,  and 
lateral  semicircular  canals;  12,  widened  mouth  of  lateral  semicircular  canal  opening  into  the 
utricle;  13,  saccule;  14,  macula  acustica  of  the  saccule;  15,  endolymphatic  duct;  16,  utriculo- 
saccular duct;  17,  ductus  reuniens;  18,  vestibular  cul-de-sac  of  cochlear  duct;  ig,  cochlear 
duct;  20,  facial  nerve;  21-24,  auditory  nerve;  21,  its  vestibular  branch;  22,  saccular  branch; 
23,  branch  to  inferior  ampulla;  24,  cochlear  branch;  25,  distribution  of  cochlear  branch 
within  the  bony  spiral  lamina. 


the  space  intervening  between  the  spiral  ligament  and  the  bony 
spiral  lamina,  thus  completely  dividing  the  bony  canal  of  the  cochlea 
into  two  parts,  an  up])er,  scala  vestibuli  (Fig.  351,  /)  and  a  lower, 
scala  tympani  (Fig.  351,  k).  These  are  perilymphatic  spaces,  the  scala 
vestibuli  communicating  with  the  perilymph  space  of  the  vestibule, 
the  scala  tympani  communicating  with  the  perivascular  lymph  spaces 
of  the  \eins  of  the  cochlear  duct.  The  scala  vestibuli  and  the  scala 
tym])ani  communicate  with  each  other  in  the  cu])()la  l)y  means  of  a 
minute  canal,  the  Jielicoirema. 

The  Cochlear  Duct  {Membranous  Cochlea  or  Scala  Media). — 
This  is  a  narrow,  membranous  tube  lying  near  the  middle  of  the 
bony  cochlear  canal  and  following  its  s]Mral  turns  from  the  vcstiljule. 


524 


THE  ORGANS. 


where  it  is  connected  with  the  saccule  through  the  canalis  reuniens, 
to  its  bhnd  ending  in  the  cupola.  It  is  triangular  in  shape  on  trans- 
verse section,  thus  allowing  a  division  of  its  walls  into  upper,  outer, 
and  lower  (Fig.  351,  Dc). 

The  upper  or  vestibular  wall  is  formed  by  the  thin  membrane  of 
Reissner   (Fig.   351,   h)   which  separates  the  cochlear  duct  from  the 


Fig.  351. — Section  through  a  Single  Turn  of  the  Cochlea  of  a  Guinea-pig.  (Bohm 
and  von  Davidoff.)  a,  Bone  of  cochlea;  I,  scala  vestibuli;  Dc,  scala  media  or  cochlear  duct; 
k,  scala  tympani;  b,  membrane  of  Reissner;  d,  membrana  tectoria  or  membrane  of  Corti; 
/,  spiral  prominence;  g,  organ  of  Corti;  h,  spiral  ligament;  i,  basilar  membrane  (outer 
portion — zona  pectinata — covered  by  cells  of  Claudius);  z,  stria  vascularis;  v,  external 
spiral  sulcus;  r,  crista  basilaris;  s,  membranous  spiral  lamina;  x,  bony  spiral  lamina; 
m,  spiral  limbus;  n,  internal  spiral  sulcus;  o,  medullated  peripheral  processes  (dendrites) 
of  cells  of  spiral  ganglion  passing  to  the  organ  of  Corti;  p,  spiral  ganglion;  q,  blood-vessel. 


scala  vestibuli.  The  mcml;rane  consists  of  a  thin  central  lamina  of 
connecti\'e  tissue  covered  on  its  \'estibular  side  by  the  vestibular  en- 
dothelium, on  its  cochlear  side  by  the  epithelium  of  the  cochlea. 

The  outer  wall  of  the  cochlear  duct  is  formed  by  the  spiral  liga- 
ment, which  is  a  thickening  of  the  periosteum.  The  outer  part  of 
the  spiral  ligament  consists  of  dense  fibrous  tissue,  its  projecting 
part   of   nifjre   loosely  arranged   tissue.     From   it,   two   folds  project 


THE  ORGANS  OF  SPECIAL  SENSE.  525 

slightly  into  the  duct.  One,  the  crista  basilar  is  (Fig.  351,  r),  serves 
for  the  attachment  of  the  membranous  spiral  lamina;  the  other,  the 
spiral  prominence  (Fig.  351,  /),  contains  several  small  veins.  Be- 
tween the  two  projections  is  a  depression,  the  external  spiral  sulcus 
(Fig.  351,  V).  That  part  of  the  spiral  ligament  between  the  spiral 
prominence  and  the  attachment  of  Reissner's  membrane  is  known  as 
the  stria  vascularis  (Fig.  351,  z).  It  is  lined  with  granular  cuboidal 
epithelial  cells,  which,  owing  to  the  absence  of  a  basement  membrane, 
are  not  sharply  separated  from  the  underlying  connective  tissue. 
For  this  reason  the  capillaries  extend  somewhat  between  the  epithe- 
lial cells,  giving  the  unusual  appearance  of  a  vascular  epithelium. 

The  lower  or  tympanic  wall  of  the  cochlear  duct  has  an  extremely 
complex  structure.  Its  base  is  formed  by  the  already  mentioned  bony 
and  membranous  division-wall  between  the  scala  media  and  the  scala 
tympani  (bony  spiral  lamina  and  membranous  spiral  lamina). 

The  bony  spiral  lamina  has  been  described  (page  523). 

The  membranous  spiral  lamina  consists  of  a  substantia  propria  or 
basilar  membrane,  its  tympanic  covering,  and  its  cochlear  covering. 

The  basilar  membrane  (Fig.  351)  is  a  connective-tissue  mem- 
brane composed  of  fine  straight  fibres  which  extend  from  the  bony 
spiral  lamina  to  the  spiral  ligament.  Among  the  fibres  are  a  few 
connective-tissue  cells.  On  either  side  of  the  fibre  layer  is  a  thin, 
apparently  structureless  membrane. 

The  tympanic  covering  of  the  basilar  membrane  consists  of  a  thin 
layer  of  connective  tissue — an  extension  of  the  periosteum  of  the  spiral 
lamina — covered  over  by  a  single  layer  of  flat  endothelial  cells. 

The  cochlear  covering  of  the  basilar  membrane  is  epithelial.  Owing 
to  the  marked  difference  in  the  character  of  the  epithelium,  the  basilar 
membrane  is  divided  into  an  outer  portion,  the  zona  pectinaia  (Fig.  351, 
/)  and  an  inner  portion,  the  zona  tecta  (Fig.  351,  s).  The  epithelium 
of  the  former  is  of  the  ordinary  columnar  type;  that  of  the  latter  is  the 
highly  differentiated  neuro-epithelium  of  Corti's  organ. 

The  Organ  of  Corti. — The  spiral  organ  or  the  organ  of  Corti  (Fig. 
351,  g,  and  Fig.  352)  is  a  neuro-epithelial  structure  running  the  entire 
length  of  the  cochlear  canal  with  the  exception  of  a  short  distance  at 
either  end.  It  rests  upon  the  membranous  portion  of  the  spiral  lamina, 
and  consists  of  a  complex  arrangement  of  four  dift'erent  kinds  of  epithe- 
lial cells.  These  are  known  as :  ( i )  pillar  cells,  (2)  hair  cells,  (3)  Deiter's 
cells,  and  (4)  Hensen's  cells  (Fig.  352). 

(i)   The   pillar   cells    arc  di^•^ded  into  outer  pillar  cells  and  inner 


526 


THE  ORGANS. 


pillar  cells.  They  are  sustentacular  in  character.  Each  cell  consists 
of  a  broad  curved  protoplasmic  base  which  contains  the  nucleus,  and 
of  a  long-drawn-out  shaft  or  pillar  which  probably  represents  a  highly 
specialized  cuticular  formation.  The  end  of  the  pillar  away  from  the 
base  is  known  as  the  head.  The  head  of  the  outer  pillar  presents  a 
convexity  on  its  inner  side,  which  fits  into  a  corresponding  concavity 
on  the  head  of  the  inner  pillar,  the  heads  of  opposite  pillars  thus  "artic- 
ulating" with  each  other.     From  their  articulation  the  pillars  diverge, 


limhvLt 


memhraTUi  tectoria 


outer  hair-cells 


iierve  Jihres 


inner  rod    vas    basilar         outer    ceUs  of  Deitera 
iqdralc    membrane     rod 


Fig.  352. — Semidiagrammatic  Representation  of  the  Organ  of  Corti  and  Adjacent 
Structures  (Merkel-Henle.)  a.  Cells  of  Hensen;  b,  cells  of  Claudius;  c,  internal  spiral  sulcus; 
X,  Nuel's  space.  The  nerve  fibres  (dendrites  of  cells  of  the  spinal  ganglion)  are  seen  pass- 
ing to  Corti's  organ  through  openings  (foramina  nervosa)  in  the  bony  spiral  lamina. 
The  black  dots  represent  longitudinally-running  branches,  one  bundle  lying  to  the  inner 
side  of  the  inner  pillar,  a  second  just  to  the  outer  side  of  the  inner  pillar  within  Corti's 
tunnel,  the  third  beneath  the  outer  hair  cells. 


SO  that  their  bases  which  rest  upon  the  basilar  membrane  are  widely 
separated.  There  are  thus  formed  by  the  pillars  a  series  of  arches 
known  as  Corti's  arches,  enclosing  a  triangular  canal,  Corti's  tunnel. 
This  canal  is  filled  with  a  gelatinous  substance  and  crossed  by  delicate 
ncr\c  llljrils.  As  the  outer  pillar  cells  are  the  larger,  they  are  fewer 
in  number,  the  estimated  number  in  the  human  cochlea  being  forty- 
five  hundred  of  the  outer  cells  and  about  six  thousand  of  the  inner  cells. 
(2)  The  hair  cells  or  auditory  cells  lie  on  either  side  of  the  arches 
of  Corti,  and  are  thus  divided  into  inner  hair  cells  and  outer  hair 
cells.  Both  inner  and  outer  hair  cells  are  short,  cylindrical  elements 
which  do  not  extend  to  the  basilar  membrane.  Each  cell  ends  below 
in  u  point,  while  from  its  free  surface  are  given  off  a  number  of  fine  stiff 
hairs. 


THE  OR(iANS  OF  SPECIAL  SENSE.  527 

The  inner  hair  cells  lie  in  a  single  layer  against  the  inner  side  of 

the  inner  pillar  cells,  one  hair  cell  resting  upon  about  every  two  pillars. 

The  outer  hair  cells  lie  in  three  or  four  layers  to  the  outer  side  of 

the   outer   pillar  cells,  being  separated  from  one  another  by  susten- 

tacular  cells,  the  cells  of  Deiter,  so  that  no  two  hair  cells  come  in  contact. 

(3)  Deiter' s  Cells  (Fig.  352). — These  like  the  pillar  cells  are  sus- 
tentacular.  Their  bases  rest  upon  the  basilar  membrane,  where  they 
form  a  continuous  layer.  Toward  the  surface  they  become  separated 
from  one  another  by  the  hair  cells.  The  long  slender  portions  of  the 
Deiter's  cells,  which  pass  in  between  the  hair  cells,  are  known  as  pha- 
langeal processes.  Between  the  innermost  of  the  outer  hair  cells  and 
the  outer  pillar  is  a  space  known  as  N'ttePs  space  (Fig.  352,  :v). 

(4)  Hensen's  Cells  (Fig.  352,  a). — These  are  sustentacular  cells, 
which  form  about  eight  rows  to  the  outer  side  of  the  outermost  Deiter's 
cells.  These  cells  form  the  outer  crest  of  Corti's  organ  and  conse- 
quently have  a  somewhat  radial  disposition,  their  free  surfaces  being 
broad,  their  basal  ends  narrow.  They  decrease  in  height  from  within 
outward,  and  at  the  end  of  Corti's  organ  become  continuous  with  the 
cells  of  Claudius  (Fig.  352,  h),  the  name  given  to  the  cochlear  epithelium 
covering  the  basal  membrane  to  the  outer  side  of  Corti's  organ. 

The  phalangeal  processes  of  the  Deiter's  cells  are  cemented  to- 
gether and  to  the  superficial  parts  of  the  outer  pillars  in  such  a  man- 
ner as  to  form  a  sort  of  cuticular  membrane,  the  lamina  reticularis, 
through  which  the  heads  of  the  outer  hair  cells  project.  This  mem- 
brane also  extends  out  as  a  cuticula  over  the  cells  of  Hensen  and  of 
Claudius. 

The  Membrana  Tectoria. — This  is  a  peculiar  membranous  structure 
attached  to  a  projection  of  the  bony  spiral  lamina  known  as  the  spiral 
limbiis  (Fig.  352),  the  concavity  beneath  its  attachment  being  the 
internal  spiral  sulcus  Fig.  352,  c).  The  membrane  is  non-nucleated 
and  shows  line  radial  striations.  It  bridges  over  the  internal  spiral 
sulcus  and  ends  in  a  thin  margin,  which  rests  upon  Corti's  organ  just 
at  the  outer  limit  of  the  outer  hair  cells. 

Blood-vessels. — The  arteries  consist  of  two  small  branches  of  the 
auditory — one  to  the  bony  labyrinth,  the  other  to  the  membranous 
labyrinth.  The  latter  divides  into  two  branches — a  vestibular  and  a 
cochlear.  The  vestibular  artery  accompanies  the  branches  of  the  audi- 
tory nerve  to  the  utricle,  saccule,  and  semicircular  canals.  It  supplies 
these  parts,  giN'ing  rise  to  a  capillary  network,  which  is  coarse  meshed 
except  in  the  crista?  and  macula?,  where  the  meshes  are  tine.     The 


528  THE  ORGANS. 

cochlear  artery  also  starts  out  in  company  with  the  auditory  nerve, 
but  accompanies  it  only  to  the  first  turn  of  the  cochlea.  Here  it  enters 
the  modiolus  where  it  gives  off  several  much  coiled  branches,  the  glo- 
merular arteries  of  the  cochlea.  Branches  from  these  pierce  the 
vestibular  part  of  the  osseous  spiral  lamina  and  supply  the  various 
structures  of  the  cochlear  duct.  The  veins  accompany  the  arteries, 
but  reach  the  axis  of  the  modiolus  through  foramina  in  the  tympanic 
part  of  the  bony  spiral  lamina. 

Lymphatics. — The  scala  media  contains  endolymph  and  is  in 
communication  with  the  subdural  lymph  spaces  by  means  of  the  endo- 
lymphatic duct,  the  endolymphatic  sac,  and  minute  lymph  channels 
connecting  the  latter  with  the  subdural  spaces.  The  perilymph  spaces 
— scala  tympani  and  scala  vestibuli — are  connected  with  the  pial 
lymph  spaces  by  means  of  the  perilymphatic  duct.  Lymph  spaces 
also  surround  the  vessels  and  nerves.  These  empty  into  the  pial 
lymphatics. 

Nerves. — The  vestibular  branch  of  the  auditory  nerve  divides  into 
branches  which  supply  the  saccule,  utricle,  and  semicircular  canals, 
where  they  end  in  the  maculae  and  cristas  as  described  on  page  521. 
The  ganglion  of  the  vestibular  branch  is  situated  in  the  internal  audi- 
tory meatus.  The  cochlear  branch  of  the  auditory  nerve  enters  the 
axis  of  the  modiolus,  where  it  divides  into  a  number  of  branches  which 
pass  up  through  its  central  axis.  From  these,  numerous  fibres  radiate 
to  the  bony  spiral  laminae,  in  the  bases  of  which  they  enter  the  spiral 
ganglia  (Fig.  351,  ^). 

The  cells  of  the  spiral  ganglia  are  peculiar,  in  that  while  of  the 
same  general  type  as  the  spinal  ganglion  cell  they  maintain  their 
embryonic  bipolar  condition  (see  page  376)  throughout  life.  Their 
axones  follow  the  already  described  course  through  the  modiolus  and 
thence  through  the  internal  auditory  meatus  to  their  terminal  nuclei  in 
the  medulla  (.see  page  441).  Their  dendrites  become  medullated  like 
the  dendrites  of  the  spinal  ganglion  cells  and  ]jass  outward  in  bundles 
in  the  bony  spiral  laminae  (Fig.  351,  0,  and  Fig.  352).  From  these 
are  given  off  branches  which  enter  the  tympanic  portion  of  the  lamina, 
where  they  lose  their  medullary  sheaths  and  ])ass  through  the  foramina 
nervosa  (minute  canals  in  the  tympanic  part  of  the  spiral  lamina)  to 
their  terminations  in  the  organ  of  Corti.  In  the  latter  the  fibres  run  in 
three  bundles  parallel  to  Corti's  tunnel.  One  bundle  lies  just  inside 
the  inner  jjillar  beneath  the  inner  row  of  hair  cells  (Fig.  352).  A 
second  Ininfllc  runs  in  the  tunnel  to  the  outer  side  of  the  inner  pillar 


THE  ORGANS  OF  SPECIAL  SENSE.  529 

(Fig.  352).  The  third  bundle  crosses  the  tunnel  (tunnel-tibres)  and 
turns  at  right  angles  to  run  between  the  cells  of  Deiter  beneath  the  outer 
hair  cells  (Fig.  352).  From  all  of  these  bundles  of  fibres  are  given  off 
delicate  terminals  which  end  on  the  hair  cells. 

Development  of  the  Ear. 

The  essential  auditory  part  of  the  organ  of  hearing,  the  membranous 
labyrinth,  is  of  ectodermic  origin.  This  first  appears  as  a  thickening 
followed  by  an  invagination  of  the  surface  ectoderm  in  the  region  of 
the  posterior  cerebral  vesicle.  This  is  known  as  the  auditory  pit.  By 
closure  of  the  lips  of  this  pit  and  growth  of  the  surrounding  mesodermic 
tissue  is  formed  the  otic  vesicle  or  otocyst,  which  is  completely  separated 
from  the  surface  ectoderm.  Diverticula  soon  appear  passing  off  from 
the  otic  vesicle.  These  are  three  in  number  and  correspond  respect- 
ively to  the  future  endolymphatic  duct,  the  cochlear  duct  and  the 
membranous  semicircular  canals.  Within  the  saccule,  utricle,  and 
ampullae  special  differentiations  of  the  lining  epithelium  give  rise  to  the 
maculag  and  cristse  acusticse.  Of  the  cochlear  duct  the  upper  and 
lateral  walls  become  thinned  to  form  Reissner's  membrane  and  the 
epithelium  of  the  outer  wall,  while  the  lower  wall  becomes  the  basilar 
membrane,  its  epithelium  undergoing  an  elaborate  specialization  to 
form  the  organ  of  Corti. 

Of  the  cochlea,  only  the  membranous  cochlear  duct  develops  from 
the  otic  vesicle;  the  scala  vestibuli,  scala  tympani,  and  bony  cochlea 
developing  from  the  surrounding  mesoderm.  The  mesodermic  con- 
nective tissue  at  first  completely  fills  in  the  space  between  the  coch- 
lear duct  and  the  bony  canal.  Absorption  of  this  tissue  takes  place, 
resulting  in  formation  of  the  scala  tympani  and  scala  vestibuli. 

During  the  differentiation  of  the  above  parts  a  constriction  appears 
in  the  body  of  the  primitive  otic  \'esicle.  This  results  in  the  incomplete 
septum  which  divides  the  utricle  from  the  saccule. 

The  middle  ear  is  formed  from  the  upper  segment  of  the  pharyngeal 
groove,  the  lower  segment  giving  rise  to  the  Eustachian  tube. 

The  external  ear  is  developed  from  the  ectoderm  of  the  first  branch- 
ial cleft  and  adjacent  branchial  arches.  The  tympanic  membrane 
is  formed  from  the  mesoderm  of  the  first  branchial  arch,  its  outer  cover- 
ing being  of  ectodermic,  its  inner  of  entodermic  origin. 

TECHNIC. 

(i)  For  the  study  of  the  general  structure  of  the  pinna  and  walls  of  the  exter- 
nal auditory  meatus,  material  may  be  fi.xed  in  formalin-^Miiller's  fluid  (technic  5, 

34 


530  THE  ORGANS. 

p.  7)  and  sections  stained  with  ha^matoxylin-eosin  (technic  i,  p.  18).  In  sections 
of  the  wall  of  the  cartilaginous  meatus  the  ceruminous  glands  may  be  studied, 
material  from  children  and  from  new-born  infants  furnishing  the  best  demonstra- 
tions of  these  glands. 

(2)  For  the  study  of  the  inner  ear  the  guinea-pig  is  most  satisfactory  on  account 
of  the  ease  with  which  the  parts  may  be  removed.  Remove  the  cochlea  of  a 
guinea-pig  with  as  much  as  possible  of  the  vestibule  and  semicircular  canals  and 
fix  in  Flemming's  fluid  (technic  7,  p.  7).  A  small  opening  should  be  made  in  the 
first  turn  of  the  cochlea  in  order  to  allow  the  fixative  to  enter  the  canal.  After 
forty-eight  hours  the  cochlea  is  removed  from  the  fixative  and  hardened  in  graded 
alcohols  (page  8).  The  bone  is  next  decalcified,  either  by  one  of  the  methods 
mentioned  on  page  9  or  in  saturated  alcoholic  solution  of  picric  acid.  If  one  of 
the  aqueous  decalcifying  fluids  is  used,  care  must  be  taken  to  carry  the  material 
through  graded  alcohols.  Embed  in  celloidin  or  parafiin,  cut  sections  through 
the  long  axis  of  the  modiolus,  through  the  utricle  and  saccule,  and  through  the 
semicircular  canals.     Stain  with  hsematoxylin-eosin  and  mount  in  balsam. 

(3)  The  neurone  relations  of  the  cristae,  maculae,  and  cochlear  duct  can  be 
demonstrated  only  by  means  of  the  Golgi  method.  The  ear  of  a  new-born  mouse 
or  guinea-pig  furnishes  good  material.  The  cochlea  together  with  some  of  the 
base  of  the  skull  should  be  removed  and  treated  by  the  Golgi  rapid  method  (page 
32).  Sections  should  be  thick  and  must  of  course  be  cut  through  undecalcified 
bone.     Good  results  are  difficult  to  obtain. 

The  Organ  of  Smell. 

The  olfactory  organ  consists  of  the  olfactory  portion  of  the  nasal 
mucosa.  In  this  connection  it  is,  however,  convenient  to  describe 
briefly  the  olfactory  bulb  and  the  olfactory  tract. 

The  Olfactory  Mucosa. — This  has  been  described  (page  264). 
The  peculiar  olfactory  cells  there  described  are  not  neuro-epithelium 
but  are  analogs  of  the  spinal  ganglion  cell,  being  the  only  example 
in  man  of  the  perij^herally  placed  ganglion  cell  found  in  certain  lower 
animals.  Each  cell  sends  to  the  surface  a  short  dendrite  which  ends 
in  several  short,  stiff,  hair-like  processes.  From  its  opposite  end  each 
cell  gives  off  a  longer  centrally  directed  process  (axone),  which  as  a 
fibre  of  one  of  the  olfactory  nerves  passes  through  the  cribriform  plate 
of  the  ethmoid  (Fig.  353,  ethm)  to  its  terminal  nucleus  in  the  olfactory 
bulb  (Fig.  353). 

Ill/'  Olfactory  Bulb. — This  is  a  somewhat  rudimentary  structure  an- 
alogous to  the  much  more  prominent  olfactory  brain  lobe  of  some  of 
the  lower  animals.  It  consists  of  both  gray  matter  and  white  matter 
arranged  in  six  fairly  distinct  layers.  These  from  below  upward  are 
as  follows:  (a)  The  layer  of  olfactory  fibres;  (b)  the  layer  of  glomeruli; 
(c)  the  molecular  layer;  (d)  the  layer  of  mitral  cells;  (e)  the  granule 


THE  ORGANS  OF  SPECIAL  SENSE. 


ry.n 


layer;  (/)  the  layer  of  longitudinal  fibre  bundles.  Through  the  centre 
of  the  last-named  layer  runs  a  band  of  neuroglia  which  represents  the 
obliterated  lumen  of  the  embryonal  lobe.  The  relations  of  these  layers 
to  the  olfactory  neurone  system  are  as  follows: 

The  layer  of  olfactory  fibres  (Fig.  353,  a)  consists  of  a  dense  plexi- 
form  arrangement  of  the  axones  of  the  above-described  olfactory  cells. 


Fig.  353. — Diagram  of  Structure  of  Olfactory  Mucosa  and  Olfactory  Bulb.  (Ramon 
y  Cajal.)  be.  Bipolar  cells  of  olfactory  mucosa;  svi,  submucosa;  ethm,  cribriform  plate 
of  ethmoid;  a,  layer  of  olfactory  fibres;  og,  olfactor}-  glomeruli;  vie,  mitral  cells;  ep,  epithe- 
lium of  olfactorv  ventricle. 


From  this  layer  the  axones  pass  into  the  layer  of  olfactory  glomeruli 
where  their  terminal  ramifications  mingle  with  the  dendritic  terminals 
of  cells  lying  in  the  more  dorsal  layers,  to  form  distinctly  outlined 
spheroidal  or  oval  nerve-fibre  nests,  the  olfactory  glomeruli  (Fig.  353,  og). 
The  latter  mark  the  ending  of  neurone  system  No.  I.  of  the  olfactory 
conduction  ])ath. 

The  molecular  layer  contains  both  small  ncr\e  cells  and  large 
nerve  cells.  These  send  their  dendrites  into  the  olfactory  glomeruli. 
The  smaller  cells  belong  to  Golgi  Type  II.  (see  page  117)  and  appear 
to  be  association  neurones  between  adjacent  glomeruli.  The  axones 
of  the  larger  cells,  the  so-called  l)rush  cells,  become  fil)res  of  the  oljac- 
orx  trad. 


532  THE  ORGANS. 

Of  the  mitral  cells  (Fig.  353,  me),  the  main  dendrites  end  in  the 
olfactory  glomeruli,  while  their  axones,  like  those  of  the  brush  cells, 
become  fibres  of  the  olfactory  tract. 

In  addition  to  the  fibres  which  pass  through  it  (axones  of  mitral 
and  of  brush  cells),  the  granular  layer  contains  numerous  nerve  cells. 
Many  of  these  are  small  and  apparently  have  no  axones  (amacrine 
cells.)  Their  longer  dendrites  pass  toward  the  periphery,  their  shorter 
dendrites  toward  the  olfactory  tract.  Larger  multipolar  cells,  whose 
axones  end  in  the  molecular  layer,  also  occur  in  the  granular  layer. 

The  layer  of  longitudinal  fibre  bundles  consists  mainly  of  the  cen- 
trally directed  axones  of  the  mitral  and  brush  cells.  These  fibres 
run  in  distinct  bundles  separated  by  neuroglia.  Leaving  the  bulb 
they  form  the  olfactory  tract  by  means  of  which  they  pass  to  their 
cerebral  terminations. 

The  brush  cells  and  mitral  cells  with  their  processes  thus  constitute 
neurone  system  No.  II.  of  the  olfactory  conduction  path. 

TECHNIC. 

(i)  Carefully  remove  the  olfactory  portion  of  the  nasal  mucosa  (if  human 
material  is  not  available,  material  from  a  rabbit  is  quite  satisfactory).  This  may 
be  recognized  by  its  distinctly  brown  color.  Fix  in  Flemming's  fluid  (technic  7, 
p.  7),  or  in  Zenker's  (technic  9,  p.  8).  Stain  thin  vertical  sections  with  htemat- 
oxylin-eosin  (technic  i,  p.  18)  and  mount  in  balsam. 

(2)  For  the  study  of  the  nerve  relations  of  the  olfactory  cells  material  should 
be  treated  by  the  rapid  Golgi  method  (page  32). 

The  Organ  of  Taste. 

The  organ  of  taste  consists  of  the  so-called  taste  buds  of  the  lingual 
mucosa.  These  have  been  mentioned  in  connection  with  the  papillae 
of  the  tongue  (page  199)  and  under  sensory  end-organs  (Fig.  268). 

The  taste  buds  are  found  in  the  side  walls  of  the  circumvallate 
papillae  (page  199),  of  some  few  of  the  fungiform  papillae,  in  the  mucosa 
of  the  posterior  surface  of  the  epiglottis,  and  especially  in. folds  (foliate 
papillae)  which  occur  along  the  ])Ostero-lateral  margin  of  the  tongue. 

The  taste  bud  (Fig.  354)  is  an  ovoid  epithelial  structure  embedded 
in  the  epithelium,  and  connected  with  the  surface  by  means  of  a  minute 
canal,  the  gustatory  canal  (Fig.  354,  a),  the  outer  and  inner  ends  of 
which  are  known,  respectively,  as  the  outer  and  inner  taste  pores. 

Each  taste  bud  consists  of  two  kinds  of  cells,  neuro-epithelial  cells 


THE  ORGANS  OF  SPECIAL  SENSE. 


533 


or  gustatory  cells  and  sustentacular  cells  (Fig.  354).  The  gustatory 
cells  are  long,  delicate,  spindle-shaped  cells  which  occupy  the  centre 
of  the  taste  bud,  each  ending  externally  ^ 

in  a  cilium-like  process,  which  usually 
projects  through  the  inner  pore.  The 
inner  end  of  the  cell  tapers  down  to  a 
fine  process,  which  may  be  single  or 
branched.  The  sustentacular  cells  are 
long,  slender  cells  which  form  a  shell 
several  cells  thick  around  the  gustatory 
cells.  Sensory  terminals  of  the  glosso- 
pharyngeal nerves  (Fig.  354,  b)  end 
within  the  taste  buds  in  a  network  of 
varicose  fibres  —  intrageminal  fibres. 
Other  sensory  terminals  of  the  same 
nerve  end  freely  in  the  epithelium  be- 
tween the  taste  buds.  These  are  finer 
and  smoother  than  the  intrageminal 
fibres  and  are  known  as  inter geminal  fibres   (Fig.   354) 


Fig.  354. — Taste-bud  from  Side 
Wall  of  Circumvallate  Papilla. 
(Merk  1-Henle.)  a,  Taste-pore; 
b,  nerve  fibres,  some  of  which 
enter  the  taste-bud — intra- 
geminal fibres;  while  others  end 
freely  in  the  surrounding  epi- 
thelium— intergeminal  fibres. 


TECHNIC. 

(i)  The  general  structure  of  the  taste  buds  is  shown  in  the  sections  of  tongue 
(technic,  p.  200). 

(2)  For  the  study  of  the  nerve  terminals  the  method  of  Golgi  should  be  used 
(page  32). 


General  References  for  Further  Study. 

Kolliker:  Handbuch  der  Gewebelehre  des  Menschen. 
McMurrich:  The  Development  of  the  Human  Body. 
Ramon  y  Cajal:  La  retine  des  vertebres.     La  Cellule,  i.x.,  li 
Schwalbe:  Lehrbuch  der  Anatomie  der  Sinnesorgane,  1887. 


INDEX. 


Abducens  (nerve  Yl),  448,  492 
Aberrant  peduncular  fibres,  470 
Absorption,  239 

of  fat,  240 
Accessorius  (nerve  XI),  431,  493 
Accessory  nasal  sinuses,  264 

olivary  nucleus,  438 
Achromatic    element    of    intranuclear 
network,  44 

spindle,  48 
Acid  aniline  dyes,  18 

cells,  219,  239 
Acidophile  granules,  97 
Acini,  190 
Acoustic  group  of  segmental  neurones, 

425 
Acrosome,  314 
Acusticus     (nerve     VIII),     425,     431, 

441,  492 
Adelomorphous  cells,  219 
Adenoids,  157 
Adipose  tissue,  85 
Adrenal,  see  Suprarenal 
Adventitia  of  arteries,  136 

of  lymph  vessels,  143 

of  veins,  138 
Afferent  peripheral  nerves,  376 
segmental  neurones,  425 

paths,  426 

pallial,   413,  414,  416,421,  422, 
428,  469,  470 

suprasegmental  neurones,  378 
Agminated  follicles,  228 
Air  cells,  274 

passages,  274 

sacs,  274,  275 

vesicles,  274 
Ala  cinerea,  430,  437 
Alcohol,  as  a  fixative,  6 

dilute,  as  a  fixative,  6 

for  hardening,  8 

Ranvier's,  4 

strong,  as  a  fixative,  6 
Alcohol-ether  celloidin,  1 1 


Alimentary  tract,  192 

development  of,  266 

endgut,  231 

foregut,  213 

headgut,  193 

midgut,  223 
Altmann's   granule   theory   of   proto- 
plasmic structure,  40 
Alum-carmine,  i  7 

for  staining  in  bulk,  19 
Alveolar  ducts,  274,  275 

glands,  187,  190 

passages,  274 

sacs,  274 
Alveoli,  190,  274  i 

Amacrine  cells,  504  1 

Amitosis,  47 
Amoeboid  movement,  46 

technic  for,  57 
Amphiaster,  48 
Amphicytes,  383 
Amphipyrenin,  43 
Amphophile  granules,  98 
Ampullae,  520 

of  Thoma,  162 
Anabolism,  45 
Anaphase,  51 
Aniline  dyes,  acid,  18 

basic,  I  7 
Anistrophic  line,  103 

substance,  103 
Annular  terminations,  388 
Annuli  fibrosi,  141 
Ansa  lenticularis,  48 1 
Anterior    corpus    quadrigemini,    466, 
465,  467,  471 

cerebral  commissure,  4  78,  481 

horns,  39S,  401, 

root    or    motor    cells    of,    380, 

perforated  space,  477,  481 
pyramids,  416 
white  commissure,  48 1 
Antrum,  ^2>, 


535 


536 


INDEX. 


Anus,  234 

Aorta,  137 

Apathy,  concerning  cilia,  68 

Appendix  epididymidis,  312 

testis,  312 

vermiformis,  232 
Aqueductus  Sylvii,  374,  462,  464 
Arachnoid  membrane,  380 
Arbor  vitae,  455 
Arborescent  terminations,  388 
Arborizations,  terminal,  112 
Arc,  neural,  377,  420 
Archipallium,  477 
Archoplasm,  45 
Arcuate  fibres,  435,  438,  447 

internal,  438,  448 
Area  tegmenti,  472 

acustica,  43  i 
Areolar  (loose)  connective  tissue,  77 
Arrector  pili  muscle,  361 
Arrectores  pilorum,  365 
Arteriae  arciformes,  294 

rectae,  296 
Arteries,  133 

adventitia  of,  136 

anterior  spinal,  406 

aorta  and  other  large,  137 

arcuate,  294 

arteriole,  134 

bronchial,  277,  279 

coats  of,  133 

coronary,  141 

development  of,  142 

elastic  tissue  of,  135,  137 

greater  arterial  circle  of  iris,  511 

hepatic,  254 

interlobar,  293 

interlobular,  294 

intima  of,  134 

large,  like  the  aorta,  137 

lesser   arterial    circle   of   the   iris, 

5'  ' 
lymjjh  channels  (jf,   139 
media  of,  135 
medium-sized,  134 
nerves  of,  139 
phrenic,  296 
posterior  spinal,  406 
precapillary,  134 
pulmonary,  277 
recurrent,  296 
renal,  286,  293 


Arteries,  small,  133 

structural  peculiarities  of  some, 

137 
sulco-commissural,  406 
suprarenal,  300 
technic  of,  139 
vasa  vasorum,  139 
Arteriole,  134 
Articular  cartilages,  180 
Articulations,  180;  see  Joints 
diarthrosis,  180 
synarthrosis,  180 
synchondrosis,  180 
syndesmosis,  180 
technic  of,  181 
Arytenoid  cartilages,  266 
Ascending  degeneration,  413 

fibre  tracts  of  spinal  cord,  413 
direct  cerebellar,  415 
Gowers',  416 
long  arms  of  dorsal  root  fibres, 

413 
posterior  columns,  414 

funiculi,  413 
spino-tectal,  415 
-thalamic,  414 
tract  of  Flechsig,  415 
tracts  forming  parts  of  afferent 
pallial  paths,  413 
to  cerebellum,  415 
tractus  spino-cerebellaris  dorsalis, 
415,  426 
ventralis,  415,  426 
uncrossed  cerebellar,  415 
Association    fibres;     see     also     Inter- 
segmental neurones 
of  brain,  425,  426 
of  cerebellum,  461 
of  cord,  399,  419 
of  endbrain,  478,  479,  483,  485 
of  isthmus,  464 
of  interbrain,  470,  472 
of  midbrain,  467 
Asters,  52 

Atresia  of  follicle,  333 
Atria,  274 
Atrophy  method  of  determining  fil)re 

tracts  of  the  cord,  413 
Attraction  sphere,  45 
Auditory  canal,  518 
cells,  526 
hairs,  522 


INDEX. 


537 


Auditory  nerve,  441,  443 

cochlear  branch   of,    439,   441, 

443 
vestibular  branch  of,  425,  438, 

441-  445.  448 
path,    425,    441,    442,    443,    470, 

485 
Auerbach,  end-buttons  of,  35 

end-feet  of,  ^s 

plexus  of,  225,  230,  232,  238 
Auricle,  518 

muscle  of,  140 
Auriculo- ventricular  ring,  140 
Axis    cj'linder,     iii,     118;     see    also 

Axone 
Axolemma,  118 

and  neurilemma,  relation  of,  120 
Axonal  degeneration,   124 
Axone,    the,  iii,  116,  375 

Bethe's  views  of,  121 

Cajal's  views  of,  120 

collaterals  of,  117 

degenerative  changes  in,  123 

development  of,  375 

fibres  of  Remak,  117 

medullary  sheath  of,  119 

naked  fibres,  117 

non-medullated,  117 

terminal  arborizations  of,  117 
Axone-hill,  1 16 

Baillarger,  line  of,  485 
Balsam,  Canada,  for  mounting,  21 
Barker,  concerning  the  neurone,  112, 

115 

Bartholin,  glands  of,  346 
duct  of,  243 

Basal  granule,  68 

Basic  aniline  dyes,  17 

Basis  pedunculi,  464,  465 

Basket  cells,  195 

Basophile  granules,  98 

Bellini,  duct  of,  289 

Berkley,    concerning   ]ntuitary   body, 
490 

Bertini,  columns  of,  28S 

Bethe,   concerning  continuity  of  ax- 
olemma and  neurilemma,  120 

Betz,  cells  of,  479,  482 

Bioblasts,  40 

Bipolar  nerve  cells,  112 

Bladder,  urinary,  298 


Blastoderm,  56 
Blastomeres,  56 
Blocking,  11 
Blood,  95 

corpuscles,  95,  99 

crenation  of  red  cells,  96 

development  of,  99 

diapedesis,  98 

dust,  99 

erythrocytes  of,  95 

granules,  elementary,  99 

granules  of  Ehrlich,  97 

hseinoglobin  of,  96 

haematin,  96 

hccmatokonia,  95 

haemolysis,  96 

Jenner's  stain  for,  28 

leucocytes  of,  96 

phagocytosis,  98 

plasma  of,  95 

platelets,  98 

red  cells  of,  95 
crenation  of,  96 
technic  for,  57 

smears,  technic  of,  100 

stroma  of,  96 

technic  of,  100 

thrombocytes,  98 

vascular  unit,  278 

white  cells  of,  96 
Blood-islands,  99,  142 
Blood-sinuses  of   hsemolymph   nodes, 

151 
Blood-vascular  unit,  278 
Blood-vessel  system,  131 

arteries,  133 

capillaries,  131 

development  of,  142 

heart,  140 

lining  of,  131 

technic  of,  139,  142 

veins,  137 
Blood-vessels,  131 

lymph  channels  of,  139 

nerves  of,  139 

technic  of,  139 
Body  cavities,  144 
Bone,  breakers,  174 

decalcification  of,   10 

formers,  173 

tissue,  92 

calcination  of,  93 


538 


INDEX. 


Bone  tissue,  cells  of,  93 

cementum,  212 

corpuscles  of,  93 

decalcification  of,  3,  9,  93 

intercellular  substance  of,  93 

lacunae  and  canaliculi  of,  93 

lamellae  of,  93 

technic  of,  94 
Bone-marrow,  168 

blood-vessels  of,  170 
red,  168 

cells  of,  168 

erythroblasts  of,  168 

fat  cells  of,  169 

leucocytes,  169 

marrow  cells,  168 

mast  cells  of,  169 

multinuclear  cells  of,  169 

myelocytes  of ,  168 

myeloplaxes  of,  169 

non-nucleated  red    blood  cells 
of,  169 

normoblasts,  168 

nucleated   red   blood   cells    of, 
168 
technic  of,  172 
yellow,  170 

endosteum,  170 

gelatinous,  170 
Bones,  166 

blood-vessels  of,  170 
cancellous  or  spongy,  164 
cells  of  origin  of,  173 
circumferential  lamella  of,  166 
development  of,   172 

intracartilaginous,  175 

intramembranous,  172 

subperichondral,  177 

subperiosteal,  177 
growth  of,  179 
hard  or  comijact,   165 
Haversian  canals  of,  165 

lamellae,  166 
Howship's  lacunae,  174 
intermediate  lamellae,   167 
interstitial  lamellae  of,  167 
lacunae,  origin  of,  173 
lymphatics  of,  171 
marrow,  168 
red,   168 
yellow,  170 
nerves  of,  171 


Bones,  nutrient  canal,  170 
foramen,  170 
vessels,  170 
osteoblasts,  173 
osteoclasts,  174 
osteogenetic  tissue,  174 
perforating  fibres,  168 
perichondrium,  175 
pericranium,  174 
periosteal  buds,  176 
periosteum  of,  167,  174 
Sharpey's  fibres,  168 
technic  of,  171 

developing  bone,  179 
Volkmann's  canals,  167,   171 
Bony  spiral  lamina,  563 
Borax-carmine,  alcoholic  solution,  20 
Born's  theory  of  corpus  luteum,  332 
Bowman,  capsule  of,  288,  290 
glands  of,   265 
membrane  of,  495 
sarcous  elements  of,  103 
Brachia  conjunctiva,  450 
Brachium  of  posterior  corpus  quad- 
rigeminum,  465 
pontis,  449 
Brain,  the,  424 

cerebral  cortex  of,  481 
contrasted  with  spinal  cord,  424 
development  of,  373 
endbrain  (telencephalon),  477 
corpus  striatum,  477,  478 
pallium,  477,  478 
rhinencephalon,  477 
forebrain  (prosencephalon) ,  468 
diencephalon     (thalamence  pha- 
lon),  468 
epithalamus,  468 
hypothalamus,  46S 
thalamus,  468 
interbrain,  468 
general  histology  of,  429 

structure  of,  424 
higher  coordinating  ajiparatus  of, 

424 
hindbrain  (rhombence phalon) ,  429 
cerebellum,  455 
isthmus,  462 
medulla,  429 
nerves  of,  429 
pons,  43  I 
tegmentum,  43  r 


INDEX. 


.'):!!) 


Brain,  membranes  of,  378 

arachnoid,  380 

blood-vessels  of,  380 

cerebral  dura,  378 

dura  mater,  378 

pia  mater,  380 

relation     of     optic     nerve     to, 
506 

technic  of,  380 
midbrain  (mesencephalon) ,  378 

aqueductus  Sylvii,  464 

basis  pedunculi,  464 

corpora   quadrigemina,    464, 
465 

iter,  464 

pes  pedunculi,  464 

substantia  nigra,  464 

tegmentum,  464 
Pacchionian  bodies  of,  171,  380 
pineal  eye,  490 
pituitary  body,  489 
relation  of,  to  optic  nerve,  506 
sand,  490 
segmental  brain  and  nerves,  377, 

425 

suprasegmental  structures,  427 

technic  of,  431,  488,  490 

ventricles,  373,  374 

vesicles,  373 
Bridges,  intercellular,  3,  66,  102 
Bronchi,  269 

blood-vessels  of,  277 

cartilages  of,  271 

development  of,  279 

lymphatics,  279 

nerves  of,  279 

primary,  269 

respiratory,  274 

structure  of  walls  of,  269 

technic  of,  280 

terminal,  272,  274 
Bruce  concerning  root  cells,  404 
Bruch,  membrane  of,  497 
Brunner's  glands,  230,  239 
Bulb,  429;  see  Medulla 
Bulbus  oculi,  494;  see  Eyeball 
Bundle  of  Lowenthal,  4  i  8 

of  Vicq  d'Azyr,  469,  477 

inferior  longitudinal,  471),  481 
Burdach,  column  of,  408,  414 

nucleus  of,  414,  430 
Bursas,  184 


Busch-Marchi  staining  inethod,  31 
Butschli's  theory  of  protoplasm  struc- 
ture, 40 
diagram  of,  41 

Cachexia  strumipriva,  282 
Cajal,  cells  of,  482 

concerning  the  neurone,  114,  120, 
121,  123 

interstitial  nucleus  of,  417,  426 

methods      for      staining      neuro- 
fibrils in  nerve  cells,  34 
Cajeput  oil  for  clearing  sections,  21 
Calcarine  area,  488 
Calcification  centre,  173,  175 

zone,  177 
Canada  balsam,  20 
Canal,  gastro-intestinal,  215 

lacrymal,  513 

of  Cloquet,  511 

of  Petit,  511 

of  Schlemm,  500 

portal,  255 
Canaliculi  of  bone,  93 

of  connective  tissue,  74 
Canalis  communis,  520 
Canalized  fibrin,  343 
Cancellous  bone,  164,  174 
Capillaries,  131 

chyle,  237 

development  of,  142 

technic  of,  139 
Capillary  endothelium,   132 

network,  132 
Capsule  of  Bowman,  288,  290 

internal,  476 

of  ganghon  cells,  s&3,  39^ 

of  Glisson,  253 

of  Tenon,  512 
Carbol-xylol    for    clearing    specimens, 

21,  28 
Carmine  alum,  17,  19 

borax,  20 

gelatin,  23 

neutral,  18 

picro-,  19 
Carotid  gland,  146 
Cartilage,  89 

arytenoid,  266 

cells,  89 

chondrin,  89 

classification  of,  90 


540 


INDEX. 


Cartilage,  cricoid,  266 
development  of,  92 
elastic,  91 
embryonal,  91 
epiphyseal,  179 
fibrous,  91 
hyaline,  90 

intercellular  matrix  of,  92 
intermediate,  179 
of  developing  bone,  175 
perichondrium  of,  92 
Santorini's,  266 
technic  of,  92 
thyreoid,  266 
tracheal,  267 
Wrisburg's,  266 
Cartilages,  articular,  180 
costal,  180 
skeletal,  180 
Caryochromes,  114 
Caudate  nucleus,  472,  478,  481 
Cavernous  sinuses,  320 
Cavity  of  embryonic  vesicle,  55 
Cedarwood  oil  as  solvent,  13 
Cell,  the,  39 

amitosis,  47 
body  of,  40 
centrosome  of,  44 
crusta  of,  42 
cytoplasm  of,  41 
deutoplasm  granules  of,  42 
division,  direct,  47 

indirect,  48 
endoplasm  of,  42 
exoplasm  of,  42 
function  of,  46 
hyaloplasm  of,  40 
intranuclear  network  of,  44 
irritability  of,  46 
islands  of  Langerhans,  250 
function  of,  25  r 
Opie's  theory  of,  251 
origin  of,  251 
structure  of,  251 
technic  of,  252 
karyoplasm  of,  4  i 
linin  of,  44 
membrane  of,  42 
metabolism  of,  45 
metaplasm  granules  of,  42 
microsomes,  40 
mitosis,  48 


Cell,  motion  of,  46 

nuclear  membrane  of,  43 

nuclein  of,  44 

nucleolus  of,  44 

nucleoreticulum,  44 

nucleus,  42 

origin  of  word,  42 

patches,  343 

paraplasm  granules  of,  42 

plastids,  41 

plastin,  40 

primary  germ-layers  of,  56 

protoplasm  of,  39 

Altmann's    granule   theory   of, 

40 
Biitschli's    foam    or    emulsion 

theory  of,  40 
fibrillar  theory  of,  40 
reproduction  of,  47 
secretory  process  of,  187 
space  (lacuna),  74 
spongioplasm  of,  40 
technic  for  study  of,  57 
trophospongium,  42 
typical,  39 

diagram  of,  39 
structure  of,  39 
vital  properties  of,  41 
Celloidin,  alcohol-ether,  1 1 
clove-oil,  I  2 
embedding,  1 1 
sections,  14 
clearing  of,  2 1 
mounting  of,  2  1 
■Cells,  acid,  219,  239 
active,  186 
adelomorphous,  219 
air,  274 

amacrine,  504,  532 
auditory,  526 
basal,  265 
basket,  195,  457 
blood,  95 
bone,  93 
brush,  53  I 
capsule,  375 
cartilage,  89,  j  77 
centro-acini,  of  Langerhans,  249 
centro-tubular,  249 
chief,  2  19,  284,  489 
chromophile,  489 
ciliated,  269 


IXDEX. 


.541 


Cells,  clear,  284 

colloid,  281 

compound  tactile,  386 

connective-tissue,  74 

corneum,  354 

crescents  of  Gianuzzi,  195 

daughter,  51 

decidual,  340 

Deiter's,  527 

delomorphous,  21Q 

demilunes  of  Heidenhain,  195 

empty,  186 

endothelial,  131 

eosinophile,  98,  152 

epithelial,  63 

erythroblasts,  168 

extrinsic,  396 

fat,  86,  169 

fibroblasts,  78 

fixed,  74 

foetal,  275,  280 

ganglia,  382 

gland,  186 

goblet,  186,  227,  269 

Golgi,  Type  I.,  117 

Type  II.,  117,  482,  531 
granule,  482 
gustatory,  533 
hair,  521,  526 
hecatomeric,  398 
Hensen's,  527 
heteromeric,  398 
interstitial,  308 
intrinsic,  396 
Kupffer's,  258 
Langerhans',  249 
leucocytes,  96,  169 
Leydig's,  513 
liver,  256 
loaded,  186 
lymphoid,  84,  148 
lutein,  329 
marrow,  168 
"last,  75,  98,  152,  169 
megalocyte,  161 
migratory  leucocytes,  226 
mitral,  530 
mononuclear,  161 
mossy,  126 

mucous,  186,  194,  227 
multinuclear,  lOi 
inuscle,  101 


Cells,  myelocytes,  168 
myeloplaxes,  169 

nerve,   11 1;  for  classification  see 
Nerve  cells 

neurilemma,  375 

neuroblasts,  iii,  126,  374 

neuro-epithelial,  522 

neuroglia,  125 

non-nucleated  red  blood,  95,  169 

normoblasts,  168 

nucleated    red    blood,    161,    168 

odontoblasts,   201,   206,    211 

of  Claudius,  527 

of  oral  glands,  194 

olfactory,  265 

osteoblasts,  173 

osteoclasts,  161,  174 

ovum,  47,  327 

oxyntic,  219 

oxyphile,  283,  285 

Paneth's,  228 

parietal,  219 

peptic,  219,  239 

phaeochromoblasts,  302 

phagocytes,  98,  152 

pigmented,  42,  64,  77 

pillar,  525 

plasma,  75 

prickle,  354,  3 5S 

primitive  ova,  324,  348 

Purkinje,  456 

red  blood,  95 

replacing,  65,  220,  227 

reserve,  281 

respiratory,  276 

resting,  49,  186,  281 

secreting,  187,  281 

serous,  194 

SertoH's,  305,  315,  340 

sex,  348 

signet-ring,  86 

simple  tactile,  386 

single  primitive,  47 

smooth  muscle,  102 

spermatids,  307,  314 

spermatocytes,  307,  314 

spermatogenic,  305 

spermatogones,  306,  314,  34g 

spider,  126 

spleen,  i6i 

supporting,  305 

sustentacular,  250,  265,  305.  521 


512 


INDEX. 


Cells,  sympathoblasts,  302 

tactile,  386 

tautomeric,  398 

thrombocytes,  98 

wandering,  75,  226 

white  blood,  96 
Cementing  glycerin  mounts,  20 
Cementum,  200,  204,  212 
Centres  of  calcification,  173 
Central  canal,  402 

chromatolysis,  124 

gelatinous  substance,  402 

gray,  431 

nervous  system,  373 

neurones,  376 

spindle,  48 

tegmental  tract,    439,    447,    454, 
464,  470 
Centriole,  45 

Centro-acinar  cells  of  Langerhans,  249 
Centrosome,  44,  48,  56 

archoplasm,  45 

attraction  sphere,  45 

centriole,  45 

daughter,  48 

of  fertilization,  56 
Centro-tubular    cells    of    Langerhans, 

249 
Cerebellar  arc,  421 

connections,  415,  417,  418,  421, 
428,  447,  449,  455 

cortex,  450,  455 

peduncles,  450 
Cerebello-olivary  fibres,  438,  439,  447 
Cerebellum,  455 

arbor  vitae,  455 

ascending  paths  to  the,  415 

association  cells  of,  461 

basket  cells  of,  457 

cells  of,  455,  456,  457 

climh)ing  fibres  of,  460 

cortex  of,  450,  455 

dentate  nucleus  of,  418,  450,  455 

development  of,  374 

fibres  of,  458,  460 
climbing,  461 
mossy,  460 
of  Bergmann,  462 
parallel,  458 

general  histology  of,  455 

granular  layer,  455 

gray  matter  of,  455 


Cerebellum,  heinispheres  of,  449,  455 

internal  nuclei  of,  450,  455 

laminae  of,  455 

middle  peduncle  of,  455 

molecular  layer,  455 

neuroglia  of,  462 

nuclear  layer,  455 

nucleus  dentatus,  450 
emboliformis,  450,  455 
globosus,  450,  455 
tecti  or  fastigii,  418,  450,  455 

peduncles  of,  455 

Purkinje  cells  of,  429,  455 

technic  of,  488 

vermis,  415,  449,  455 
Cerebral  arc,  421 

cortex,  481 

hemispheres,  477 

development  of,  374 

membranes,  378 

peduncles,  464 

vesicle,  373 
Cerebro-spinal  ganglia,  375,  382 
technic  of,  394 

nervous   system,   373; 

see  Nervous  system  {cerebro- 
spinal) 

neurones,  efferent  peripheral,  395 
Ceruminous  glands,  518 
Cervical  enlargement  of  cord,  396 

segments  of  cord,  396 
Cervix,  337 

epithelium  of,  338 

external  os,  338 

of  posterior  horns,  402 

ovula  Nabothi,  338 

plicae  palmatae,  338 

technic  of,  349 
Cheeks,  mucous  membrane  of,  193 
Chemotaxis,  46 
Chiasma,  optic,  504 
Chief  cells,  219,  489 
Chloride  of  gold  for  staining  connect- 
ive-tissue cells,  26 
Chloroform  as  solvent,  13 
Choledochus  ductus,  263 
Choriocapillaris,  497 
Chorion,  341 
Chorionic  villi,  341 
Chorioid,  the,  496 

choriocapillaris  of,  497 

ciliary  body  of,  498 


INDEX. 


543 


Chorioid,  fissure,  516 

Haller's  layer  of,  407 

iris,  500 

lamina  citrea,  497 

suprachorioidea,  497 
perichorioidal   lymph    spaces   of, 

497 
plexus,  431,  437.  45° 
tapetum  cellulosum  of,  497 

fibrosum  of,  497 
venae  vorticosse  of,  497 
vitreous  membrane  of,  49S 
Chromaffin  granules,  299 
Chromatic     element    of    intranuclear 

network,  44 
Chromatin,  44 
Chromatolytic  changes,  333 
Chromatolysis,  124 
Chrome-silver  method  of  Golgi,  26 
Chromophilic  bodies,  113,  114 

significance  of,  115,  121 
Chromosomes,  50 
Chyle  vessels',  237 
Cilia,  47,  63,  68 
Ciliary  artery,  511 
body, 498 

blood-vessels  of,  5 1 1 
canal  of  Schlemm,  500 
ligamentum  pectinatum,  500 
muscles  of,  499 
ora  serrata  of,  498,  501 
pars  ciliaris  retinae,  499 
processes  of,  498 
spaces  of  Fontana,  500 
vitreous  membrane  of,  499 
ganglion,  390 
movement,  47 

technic  for,  457 
muscle,  499 
plexus,  512 
processes,  498 
Cingulum,  479 
Circulatory  system,  131 

blood-vessel  system,  131 

carotid  gland,  146 

coccj'geal  gland,  146 

development  of,  142 

general     references     for     further 

study,  146 
lymph-vessel  system,  143 
Circumferential  lainellae,  167 
Circum vallate  papillae,   ig7 


Cirl,     concerning    fibres     of    internal 

capsule,  472 
Clarke's  columns,  408,  415 
Claudius,  cells  of,  527 
Clava,  the,  430 
Clearing  specimens  before  mounting, 

2  I 
Clefts  of  Schmidt-Lantermann,  119 
Climbing  fibres,  404 
Clitoris,  346 

Closed  skein  (spireme),  49 
Cloquet's  canal,  511 
Clove-oil  celloidin,  12 
Coagulum  sheath,  120 
Coccygeal  glands,  143 

segments  of  spinal  cord,  396 
Cochlea,  522 

bony  spiral  lamina  of,  523 

cupola  of,  523 

hamulus  of,  523 

helicotrema,  523 

membranous  spiral  ligament  of, 

523 
modiolus  of,  522 
scala  tympani,  523 

vestibuli,  523 
spiral  ligament  of,  523 
Cochlear  duct,  523 

basilar  membrane  of,  525 
crista  basilaris,  525 
external  spiral  sulcus,  525 
membrane  of  Reissner,  524 
organ  of  Corti,  525 
spiral  prominence  of,  525 
stria  vascularis,  525 
zona  pectinata,  525 
tecta,  525 
nerve,  439,  441 
tracts,  450,  453,  465 
Coelom,  144 
Cohnheim's  field,  103 
Collaterals,  117 
CollicuH,  364,  365,  374 
Colloid,  281,  284 
Colostrum  corpuscles,  370 
Column  cells,  398 

hecateromeric,  3 98 
heteromeric,  398 
tautomeric,  398 
technic  of,  399 
of  Burdach,  408,  414 
of  GoU,  40S,  4  1  4 


544 


INDEX. 


Columnas  rectales,   234 
Columns  of  Bertini,  2 88 

of  Sertoli,  305 
Comma  tract  of  Schultze,  419 
Commercial  formalin,  4 
Commissura  habenularis,  477 
Commissural  fibres,  478 
Compact  bone,  165 
Compound  tactile  cells,  386 
Conduction  path,  377 

afferent  pallial,  413 

afferent  and  efferent    supraseg- 
mental,  426 

auditory,  441 

descending  suprasegmental,  433 

pallio-spino-peripheral     efferent, 

417 
to  cerebellum,  415 
Cone  association  neurones,  507 
fibres,  503 
-visual  cell,  503 
Cones,  layer  of  rods  and,  502 
Conjunctiva,  513 

end  bulbs  of,  387 
Connective  tissue,  73 
adipose  or  fat,  85 
areolar,  77 

basement  substance  of,  77 
bone,  92 
canaliculi  of,  74 
cartilage,  89 
cells  of,  75 
characteristics  of,  73 
chlorid-of-gold  method  for  dem- 
onstrating cells  of,  26 
classification  of,  74 
dense  fibrous,  77 
elastic,  78 
elastin  of,  77 

embryonal,  73,  8r,  172,   179 
fat,  85 
fibres  of,  76 

elastic,  76 

fibrillated,  76 

reticular,  76 

white,  76 

yellow,  76 
fibrillar,  74 
fibroblasts,  78 
fixed  cells  of,  74 
formed,  78 
gelatin  of,  76 


Connective  tissue,  histogenesis  of,  73 

intralobular,  188 

interalveolar,  277 

intercellular  substance  of,  76 

interlobar,  188 

interlobular,  87,  89,  188 

intrafascicular,  184,  382 

lacunae  of,  74 

lymphatic,  84 

loose,  77 

Mallory's  stain  for,  28 

mast  cells  of,  75 

mucous,  81 

neuroglia,  94,  125 

pigmented  cells  of,  77 

plasma  cells  of,  75 

reticular,  83 

retinaculse  cutis,  353 

staining  cells  of,  26 

technic  for,  80,  83,  85,  89,  92,  94 

theories  of  development  of  fibres 
of,  78 

wandering  cells  of,  75 
Constrictions  of  Ranvier,   119 
Contact  theory  of  neurones,  122 
Continuity  theory  of  neurones,  122 
Convoluted  tubules,  288,  289,  290 
Cord,  spinal;  see  Spinal  Cord 
Corium,  351;  see  Derma 
Cornea,  the,  494 

anterior  elastic  membrane  of,  495 
epithelium  of,  495 

corpuscles  of,  49 j 

endothelium  of  Descemet  of,  496 

layers  of,  494 

membrane  of  Bowman  of,  495 
of  Descemet  of,  496 

perforating  or  arcuate  fibres  of, 
496 

posterior    elastic    membrane    of, 
496 

substantia  propria  of,  496 
Corneal  corpuscles,  496 
Cornu  ammonis,  477,  478 
Cornua  of  cord,  401 
Corona  radiata,  326,  478,  479,  481 
Coronary  arteries,  141 
Corpora  amylacea,  3  i  7 

cavernosa,  3  j  9 

lutea  of  pregnancy,  330 
spuria,  332 
vera,  330 


INDEX. 


545 


Corpora  mammillaria,  477,  478 
quadrigemina,  374,  464 
anterior,  464,  465 
development  of,  374 
posterior,  464,  465 
striata,  373 
Corpus  albicans,  330 

callosum,  478,  479,  481 
dentatum,  450 
hsemorrhagicum,  329 
Highmori,  or  mediastinum  testis, 

303 
luteum,  329 

theory  of,  332 
Luysii,  468 
quadrigeminum,  anterior,  464, 

465,  467,  510 
spongiosum,  319 
striatum,  477,  478,  481 
caudate  nucleus,  481 
putamen,  481 
subthalamicum,  468,  477 
trapezoideum,  450 
Corpuscles,  blood,  95 
colostrum,  370 
corneal,  496 
crescentic,  317 
Golgi-Mazzoni,  365 
Grandry's,  386 
Hassall's,  154 
Meissner's,  321,  365,  387 
Merkel's,  386 
Pacinian,  365,  388 
renal,  288 
Rufifini's  365 
salivar}^  157 
splenic,  159 
tactile,  365 
Vater-Pacinian,  365 
Wagner,  365 
Cortex  cerebelli,    450,    455;    see    also 
Cerebellum 
cerebri,   481;    see  also    Cerebntin 
areas  of,  4S8 
association  fibres  of,  485 
barren   or  molecular   layer  of, 

48  2 
cells  of,  481 
of  Betz,  484 
of  Cajal,  4S2 
of  Golgi,  Type  II.,  482 
of  Martinotti,  482 


Cortez    cerebri,    cells   of,    pyramidal, 
481 
commissural  fibres,  478 
corona  radiata  of,  478,  481 
deep  tangential  fibres  of,  485 
external  granular  layer,  482 
ganglionic  layer,  483 
internal  granular  layer,  482 
interradiary  plexus,  485 
layer  of  polymorphous  cells,  483 

of  pyramidal  cells  of,  481 
line  of  Baillarger,  48 5 
molecular  la^'-er,  482 
multiform  layer,  483 
plexiform  layer  of  Cajal,  482 
projection  fibres,  485 
radiations  of  Meynert,  485 
superficial,  tangential  fibres  of, 

482 
supraradiary  plexus  of,  485 
Cortical  labyrinths,  288 

P3^ramids,  288;  see  also  Kidney 
Corti's  arches,  526 

organ,     525;    see    also    Organ    of 
Corti 

tunnel,  526 
Cotyledons,  344 
Cowper's  glands,  319 

technic  of,  319 
Cox-Golgi  method  of  staining,  33 
Cranial    nerves,    380,    492;    see    also 

Xerves,  cranial 
Crenation  of  red  blood  cells,  96 
Crescentic  corpuscles,  317 
Crescents  of  Gianuzzi,   195,   244,   267 
Cretinism,  282 
Cricoid  cartilage,  266 
Crista  acustica,  522 

basilaris,  525 
Crossed  pyramidal  tracts,  416,  433 
Crura  cerebri,  465 
Crusta  (exoplasm),  42 
Crypt  of  Lieberkiihn,  228,  230 
Cumulus  ovigerus,  326 
Cupola,  523 
Cupula,  522 

Cuticle,  353;  see  Epidermis 
Cuticula,  42,  63 
dentis,  204 
Cuticular  membrane,  63,  20Q,  225 
Cystic  duct,  260 
Cytoarchitecture,  488 


546 


INDEX. 


Cytoplasm,  41 

of  nerve  cells,  112 
Cytoreticulum,  40 

Darkschewitsch,  nucleus  of,  417 
Daughter  cells,  5  i 

centrosomes,  48,  53 

chromosomes,  51 

stars,  5 1 
Decalcification,  3,  g 
Decalcifying,  9 

fluids,  10 
Decidua  basalis,  340 

capsularis,  340 

graviditatis,  340 

menstrualis,  339 

placentalis  subchorialis,  344 

reflexa,  340 

serotina,  340 

vera,  340 
Decidual  cells,  340 
Decolorizing      fluid       for      Weigert's 

hsematoxylin,  30 
Decussation  of  fillet,  435 

optic,  507 

of  Forel,  467 

of  Meynert,  467 

of  pyramids,  416,  429,  431 

sensory,  435 
Degenerating         nerves,  Marchi's 

method  for  staining,  3  i 
Dehiscent  glands,  190 
Deiter's  cells,  527 

nucleus,  418,  426,  448 

descending  tract  from,  418 
Delafield's  hsematoxylin,  15 
Delomorphous  cells,  219 
Demilunes  of  Heidenhain,   195 
Dendrites,  the,  iii,  116,  375 
Dental  canals,  201,  21  r 

germ,  206 

jjapilla,  206 

periosteum,  205 

ridge,  208 

sac,  208 

sheath,  Neumann's,  203 

shelf,  206 
Dentate  nucleus,  418 
Dentinal  fibres,  201 

jmlp,  20 r 
Dentine,  201,  210 

chemical  com]K;sitif)n  of,  201 


Dentine,  development  of,  210 
Derma,  or  corium,  351 

corpuscles  of  Meissner,  387 

muscle  cells  of,  352 

papillae,  compound,  352 
nerve,  356 
simple,  352 
vascular,  352 

pars  papillaris,  352 
reticularis,  351 

pigmentation  of,  355 
Descemet,  endothelium  of,  496 

membrane  of,  496 
Descending  degeneration,  413 

fibre   tracts    of   the   spinal   cord, 
416;  see  Fibre  tracts  of  spinal 
cord  {descending) 
Deutoplasm,  42,  328 
Development  of  bone,  172 

technic  of,  i  79 
Diapedesis,  98 
Diaphysis  of  bone,  179 
Diarthrosis,  180 

articular  cartilages,  180 

glenoid  ligaments,  181 

interarticular  cartilages,   181 

joint  capsule,  181 
Diaster,  50,  51,  54 
Diencephalon,  373,  468 
Digestive  system,  192 

alimentary  tract  of,  192 

development  of,  262 

endgut,  231 

foregut,  2  13 

gall-bladder,  261 

general     references    for     further 
study,  263 

headgut,  193 

large  intestine,  231 

larger  glands  of,  242 

liver,  253 

mesentery,  235 

midgut,  223 

mouth,  193 

oesophagus,  213 

omentum,  235 

jjancreas,  247 

])ancreas,  247 

jjharynx,  212 

peritoneum,  235 

rectum,  234 

salivary  glands,  242 


IXDKX. 


.'a: 


Digestive  system,  small  intestine,  223 

stomach,  217 

teeth,  200 

tongue,  ig6 

vermiform  appendix,  232 
Direct  cerebellar  tract,  415 

pyramidal  tract,   417 
Discus  proligerus,  326 
Dissociation  of  tissue  elements,  4 
Distal  convoluted  tubule,  287 
Disynaptic  arc,  421 
Dogiel's  end  plates,  320,  512 

theory  of  structure  of  spinal  gan- 
glion, 383 
Dorsal  accessory  olivary  nucleus,  438 

decussation  of  Meynert,  465 

graj?^  commissure,  402 

root  fibres  of  white  matter,  403 

spino-cerebellar  tract,  414 

white  commissure,  403 
Duct  systems  of  glands,  igo 
Ducts,  aberrans  Halleri,  311 

alveolar,  274 

Bartholini's,  244 

Bellini's,  289,  292 

choledochus,  263 

cochlear,  523 

coinmon,  260 

excretory,  of  glands,  190 

cystic,  260 

endolymphatic,  521 

ejaculatory,  311 

excretory,  1S7 

Fallopian  tube,  334 

Gartner's,  333 

hepatic,  255 

mesonephric,  347 

Miillerian,  3  18 

nasal,  513 

of  Miiller  (embryonal),  312 

of  sweat  glands,  355 

oviduct,  334 

pancreatic,  247 

pronephric,  347 

reuniens,  521 

Santorini's,  247,  266 

secondary  pancreatic,  247 

seminal,  309 

Stenoni's,  243 

thoracic,  143 

thyreo-glossal,  283 

utriculo-saccular,  ^21 


Ducts,  vas  deferens,  304,  310 

epididymis,  309 

vas  efferentia,  309 

Wharton's,  244 

Wirsung's,  247 

Wolffian,  347 
Ductus  aberrans  Halleri,  3  1 1 

reuniens,  521 
Duodenum,  230 

Brunner's  glands,  241 
technic    of. 
Dura  mater,  378 

blood-vessels  of,  380 

cerebral,  378 

spinal,  379 

technic  of,  380 
Dyes,  basic  aniline,  i  7 

nuclear,  1 5 

plasma,  17 
Dynamic  centre  of  cell,  52 

Ear,  development  of,  521; 
drum,  518 
external,  518 

auricle,  518 

blood-vessels  of,  519 

ceruminous  glands  of,  518 

ear  drum,  518 

external  auditory  canal,  518 

lymphatics  of,  519 

nerves  of,  519 

pinna,  518 

tympanic  membrane,  578 
internal,  520 

ampulla,  520 

blood-vessels  of,  527 

canalis  communis,  520 

cochlea,  520 

ducts  of,  521 

ductus  reuniens,  521 

endolymph  of,  520 

endolymphatic  duct,  521 
sac,  521 

fenestra  ovalis,  520 
rotunda,  520 

lymphatics  of,  5 28 

membrana  tectoria.  527 

membranous  labyrinth,    520 

nerves  of,  528 

organ  of  Corti,  325 

osseous  labyrinth  of,  520 

perilymph  of,  520 


)48 


INDEX. 


Ear,  internal,  saccule,  521 

semicircular  canals,  522 
utricle,  521 

utriculo-saccular  duct,  521 
vestibule,  520 
middle,  or  tympanum,  519 
fenestra  rotunda  of,  519 
ossicles  of,  520 
stapes,  520 
wax,  518 
Ebner's  glands,  199 
Ectoderm,  56 

tissue,  derivations  from,  61 
Edinger-Westphal  nucleus,  465 
Effectors,  375,  424,  426 
Efferent  pallial  paths,  413,   414,   416, 

421,  422,  428,  469,  470 
Egg  cords,  Pfiiiger's,  324 
technic  of,  336 
nests,  325 
Ehrlich,  granules  of,  97 
Ejaculatory  ducts,  311 
Elastic  cartilage,  91 
tissue,  78 

Weigert's  stain  for,  26 
Elastin,  77 
Eleidin,  354 

Ellipsoid  of  Krause,  503 
Ellipsoids  of  spleen,  161 
Embedding,  10 
celloidin,  1 1 
paraffin,  12 
Embryonal  tissue,  73,  81 

fat  tissue,  86 
Eminentia  hypoglossi,  437 

medialis,  430 
Emvilsion     theory     of     protoplasmic 

structure,  40 
Enamel,  200,  206,  208 
cells,  209 

chemical  composition  of,  204 
development  of,  206,  208 
fibres,  204 
organ,  206,  208 
prisms,  204,  209 

lines  of  Retzius  of,  204 
Endbrain  {telencephalon) ,  373,  477 
corpus  striatum,  478 
pallium,  478 

neopallium,  478,  470 
olfactory  pallium,  477,  478 
rhinence]jhalon,  477 


Endbrain,  anterior  perforated  space, 

477 

gyrus  hippocampi,  477 

olfactory  bulb,  477 
nerve,  477 

pyriform  lobe,  477 

trigonum  olfactorium,  477 

tuberculum  olfactorium,  477 
End-buttons,  456 

of  Auerbach,  35 

-feet  of  Auerbach,  35 

-bulbs,  385,  387 
of  Krause,  321 
Endgut,  231 

large  intestine,  231 

mesentery,  235 

peritoneum,  235 

omentum,  235 

rectum,  234 

vermiform  appendix,  232 
Endocardium,  141 
Endochondral  ossification,  172,  175 
Endolymph,  520 
Endolymphatic  duct,  521 

sac,  521 
Endomysium,  184 
Endoneurium,  117,  382 
Endoplasm,  42 
Endosteum,  170 
Endothelial  tube,  143 
Endothelium,  70 

of  Descemet,  496 
Engelmann,   showing  ciliated  epithe- 
lial cell,  69 
Entoderm,  56 

tissue  derivations  fron-1,61,262,279 
Eosin,  17 

-glycerin,  20 

-hsematoxylin  stain,  18 
Eosinophile  granules,  98,  152,  489 
Epiblast,  56 
Epicardium,  141 
Ejjicranium,  174 
E])idermis  (or  cuticle),  353 

eleidin,  354 

keratin,  354 

keratohyaline  granules,  354 

mitosis  of  cells  of,  354 

pareleidin,  355 

pigmentation  of,  355 

jmckle  cells  of,  354 

stratum  corneum  of,  354 


INDEX. 


549 


Epidermis  stratum  corneum  of,  cylin- 
dricum  of,  353 

germinativum  of,  353 
granulosum  of,  354 
lucidum  of,  354 
Malpighii  of,  353 
mucosum  of,  353 
spinosum  of,  354 
Epididymis,  309 
cells  of,  309 
vas  epididymis  of,  309 
vasa  efferentia  of,  309 
Epidural  space,  338 
Epiglottis,  266 
Epimysium,  183 
Epineurium,  381 
Epiphyseal  cartilage,  179 
Epiphysis  of  bone,  179 
Epithalamus,  468,  477 
Epithelium,  63 

basal  membrane  of,  63 
ciliated,  68 
classification  of,  64 
cuboidal,  65 

cuticular  membrane  of,  63 
endothelium,  70 
follicular,  326,  327,  31,3 
general  characteristics  of,  63 
germinal,  324,  348 
glandular,  69,  186 
histogenesis  of,  63 
intercellular  bridges  of,  63 
lens,  510 

membrana  propria  of,  63 
mesothelium,  70 
neuro-,  69 
pigmented,  69 
pseudo-stratified,  65 
replacing  cells  of,  65 
respiratory,  275 
simple,  64 
columnar,  65 
pseudo-stratified,  65 
squamous,  64 
stratified,  66 
columnar,  67 
squamous,  66 
transitional,  67 
surface,    of  mucous   membranes. 


191 
syncytium,  343 
tactile  cells  of,  ^ 
technic  of,  7 1 


86 


Eponj^chium,  358 
Epoophoron,  333 
Erectile  tissue,  319,  346 
Ergastoplasm,  102 
Erythroblasts,  168 
Erythrocytes,  95 
Erythrosin,  18 
Eustachian  tube,  519,  520 
Excretory  ducts,  187 

substances  in  cells,  42 
Exoplasm,  42,  78 
External  arcuate  fibres,  435,  438,  447 

ear,  518;  see  Ear,  external 

OS,  338 

spiral  sulcus,  525 
Extero-ceptors,  390 
Eye,  the,  494;  see  Organ  of  vision 

pineal,  490 
Eyeball  (or  bulbus  oculi),  494 

blood-vessels  of,  511 

chorioid  of,  496 

ciliary  body  of,  498 

cornea  of,  494 

development  of,  515 

iris  of,  500 

lens,  510 

lymphatics  of,  512 

nerves  of,  501,  505,  512 

retina  of,  501 

sclera  of,  494 

technic  of,  517 
Eyelashes,  513 
Eyelid,  the,  513 

blood-vessels  of,  514 

conjunctiva  of,  513 

epidermis  of,  513 

glands  of,  513 
of  Mall,  513 

lymphatics  of,  514 

Meibomian  glands  of,  514 

muscles  of,  514 

nerves  of,  514 

tarsus  of,  513 

technic  of,  518 

Facialis  (nerve  VII),  425,  492 
Fallopian  tube,  334;  see  Oviduct 

ampulla  of,  334 

blood-vessels  of,  335 

coats  of,  334 

development  of,  346 

fimbriated  extremity  of,  334 

isthmus  of,  334 


550 


INDEX. 


Fallopian  tube,  lymphatics  of,  335 

nerves  of,  335 

ovarian  extremity,  334 

technic  of,  335 

False  corpora  lutea,  330 

Fascicles  of  muscle,  183 

of  nerves,  381 
Fasciculi,  362 

Fasciculus  arcuatus,  479,  481 
of  Thomas,  418 
medial  longitudinal,  418 
posterior  longitudinal,  43Q,  467 
perpendicular  of  Wernicke,  479 
retroflexus  of  Meynert,  477 
solitarius,  438,  439 
superior  longitudinal,  479,  481 
uncinate,  479,  481 
Fastigio-bulbar  tract,  450 
Fat,  absorption  of,  240 
technic  of,  241 
blood  supply  of,  89 
development  of,  86 

technic  of,  89 
gobules,  240 
osmic-acid  stain  for,  28 
subcutaneous,  353 
tissue,  85 

histogenesis  of,  86 
technic  of,  89 
Fat-droplets  in  cells,  43,  86 
Fat-lobules,  86 

Fauces,  mucous  membrane  of,  193 
Female  genital  organs,  323 

pronucleus,  53 
Fenestra  ovalis,  520 

rotunda,  519 
Fenestrated  membrane,  79 
Ferrein,  pyramids  of,  288 
Fertilization  of  the  ovum,  52 
Filjrae  jjropriae  of  Meynert,  479,  488 
FiVjre  baskets,  505 
systems,  377 
efferent,  380 
main  motor,  380 
shf^rt,  399,  4  I  9 

jjrojjrio-spinal,  4J9 
spino-spinal,  419 
tracts  of  cord  (ascending),  413 
direct  cerebellar,  4  1  5 
Gowers',  4 1  6 

long  ascending  arms  of  dor- 
sal root  filjres,  4  1  3 


Fibre     tracts     of     cord     (ascending), 
of  spinal  cord,  40S 
posterior  columns,  401 
spino-tectal,  415 
spino-thalamic,  414,  433 
tract  of  Flechsig,  4 1  5 
tractus     spino-cerebellaris 
dorsalis,  415,  426,  433 
ventralis,  415,  426,  433 
(descending),  416 

anterior  marginal  bundle  of 

Lowenthal,  418 
anterior  pyramids,  416 
antero-lateral,  41S 
cerebro-spinalis,  416 
comma  tract  of  Schultze,  419 
crossed  pyramidal,  416 
descending  tract   from    Dei- 

ter's  nucleus,  41S 
direct  pyramidal,  417 
fasciculus  of  Thomas,  418 
from  the  interstitial  nucleus 

of  Cajal,  417 
fundamental,  399,  419 
Helweg's,  418 

marginal    bundles    of    Low- 
enthal, 418 
origin  of  tracts,  396 
oval  bundle  of  Flechsig,  418 
pallio-spinalis,  416 
pyramidal,  416 
rubro-spinal,  417 
septo-marginal,  418 
tecto-spinal  tract,  4x7 
tract  of  Tlirck,  417;  see  Di- 
rect pyraniidal 
tractus  cortico-spinalis,   416 
vestibulo-spinal,  418 
Von  Monakow's  tract,  417 
Fil)res,   afferent  nerve,  3  7() 
arcuate,  43  5 
association  of  iJuUium,  478,  479, 

4«5 
calcified,   1  72 
cartilage,  9  1 
commissural,  478 
cone,  503 

connective-tissue,  76 
development  of,  78 
cortical,  359 
dentinal,  2  1  1 
efferent  root,  375 


INDEX. 


551 


Fibres,  enamel,  204 

external  arcuate,  435 

genioglossal,  196 

heart  muscle,  106 

intergeminal,  533 

internal  arcuate,  435 

interzonal,  50 

intrageminal,  533 

involuntary    striated     (heart) 
muscle,   1 06 

lens,  510 

Mallory's  method  of  staining  con- 
nective-tissue, 27 

mantle,  48 

Mliller's,  504 

nerve,  113;   see  also  Nerve  fibres 
meduUated,  117 
non-medullated,  117, 

neuroglia,  126 

of  areolar  tissue,  78 

of  bone,  93 

of  developing  muscle,  108 

of  formed  connective  tissue,    78 

of  Remak,  117 

of  Sharpey,  168 

olfactory,  layer  of,  530 

perforating  or  arcuate,  of  cornea, 
496 

projection,  469,  470,  478,  479 

radiate,  258 

reticulo-spinal,  418 

rod,  503 

styloglossal,   197 

superficial  arcuate,  435 

tendon,  77 

tunnel,  529 

voluntary  muscle,   102,   105 

Weigert's    method    for    staining 
elastic,  26 
method  for  staining  nerve,  29 

white  or  fibrillated,  76 

yellow  or  elastic,  74,  76 
Fibrillar  connective  tissue,  74 

theory  of  protoplasmic  structure, 
40 
Fibroblasts,  78 
Fibrous  cartilage,  91 
Fila  olfactoria,  425 
Filar  mass,  40 
Filiform  papillae,  197 
Fillet  (or  medial  lemniscus),  414,    42(1, 
435,  436,  440,  442,  44(1,  45  1 


Filum  terminale,  396 

Fimbria,  478,  481 

Fissure,  anterior  median,  401 

chorioid,  516 
Fixation,  5 

by  injection,  6 

in  toto,  6 
Fixatives,  6,  7,  8 
Flechsig,  oval  bundle  of,  418 

myelogenetic     method     of,     40S, 
488 

tract  of,  415 
Flemming     concerning      cell-division, 

47 
Flemming's  fluid,  7 
Foam  theory  of  protoplasm  structure, 

40 
Foetal  cells,  275,  280 

structures,      appendix       epididy- 
midis,  312 
of  genital  system,  312,  ^^^ 
testis,  312 
ductus  aberrans  Halleri,  311 
organ  of  Giraldes,  311 
paradidymis,  311 
Foliate  papillae,  532 
Follicle,      Graafian,      324;      see      also 

Graafian  follicle 
Follicles,  agminated,  228 

solitary,  221,  228 
Follicular   cavity   or   antrum,    325 
FoUiculi  linguales,   157;  see  Tonsils 
Fontana,  spaces  of,  500 
Foramen  caecum  lingui,  157 
Foramina  nervosa,  528 

papillaria,  289 
Forebrain  (prosencephalon) ,  373,  46S 
diencephalon  [thalamencephalon) , 
468 
epithalamus,  468 
hypothalainus,  468 
thalamus,  468 
interbrain,  468 

section  through  junction  of  mid- 
brain and  thalamus,  470 
Foregut,  the,  213 

general  structure  of  walls  of  the 

gastro-intestinal  canal,  215 
oesophagus,  213 
stomach,  2  i  7 
Forel,  decussation  of,  4(17 
tield  of,  472 


INDEX. 


Formaldehyde,  as  a  fixative,  6 

for  macerating,  4 

-bichromate  method,  7,t, 
ForinaHn,  commercial,  4 
Formalin-Miiller's  fluid  (Orth's),   7 
Fornix,  477,  47S,  481 

anterior  pillars  of,  481 

commissure,  478 
Fossa  navicularis,  322 
Fountain-like  decussation  of  Meynert, 

467 
Fourth  ventricle,  430,  435,  447 
Fovea  centralis,  505 
Fraenkel's   theory  of   corpus  luteum, 

332 
Free  endings  of  sympathetic  nerves, 

394 
Fuchsin,  i  7 
Function  of  cells,  46 
Fundamental  columns  of  spinal  cord, 

399 
Fundus  glands,  219 
Fungiform  papillae,  197 
Funiculus  cuneatus,  414 

gracilis,  414 

posterius,  413 


Gage,  showing  muscle  fibres,  106,  107 
Gage's  hsematoxylin,  15 
Gall-bladder,  261 

coats  of,  261 

mucous  membrane  of,  261 

rugse  of,  261 
Galvanotaxis,  46 
Ganglia,  382 

amphicytes,  383 

cerebral,  382 

cerebro-spinal,  375,  382 

chain,  390 

Gasserian,  393 

habenularis,  477 

of  Corti,  38 7 

of  vScarpa  of  VIII.,  425 

satellite  cells,  383 

spinal,  382 

spiral,  528 

spirale  of  VIII.,  425 

structure  of,  382 

sympathetic,  375,  390 

technic  for,  394 

vertebral,  390 


Ganglion  cells,  375 

capsule  of,  383,  392 

development  of,  375 
Gartner's  canal,  347 

duct,  333 
Gasserian  ganglion,  454 
Gastric  crypts,  218 

glands,  218 

pits,  218 
Gastro-hepatic  omentum,  235 
Gastro-intestinal  canal,  general  struc- 
ture of  the  walls  of,  215 
Gelatin,  76 

carmine  for  injecting,  23 

Prussian  blue,  for  injecting,  23 
Gelatinous  marrow,  170 

substance  of  Rolando,  402 
Gemmules,  456 
Geniculate  body,  465,  470 

ganglion  of,  VII.,  425 
Genio-glossal  fibres,  196 
Genital  gland,  348 

ridge,  348 

system,   303;   see  also  Reproduc- 
tive system 
development  of,  346 
rudimentary     structures     con- 
nected with  development  of, 

3ii>  333.  346 
Genito-urinary   system,    see    Urinary 
system,    286,   and    Reproduc- 
tive system,  303 
Gennari,  line  of,  488 
Gentian  violet,  17 
Genu-facialis,  431,  448 
Germ  hill,  326 
layers,  56 

tissues  derived  from,  61 
Germinal  epithelium,  324,  348 
spot,  327 
vesicle,  53,  327 
Giant  cells  of  Betz,  482,  484 
Gianuzzi,  crescents  of,  195,  244,  267 
Giraldes,  organ  of,  311,  347 
Gland  cells,  186 
Glands,  186 

acini  of,   1  90 
alveolar,  187,  J90 
compound,  188,  190 
simple,   188,  s()0 
alveoli  of,  j  87,  j  90 
Bartholin's,  346 


INDEX. 


553 


Glands,  Bowman's,  263 
Brunner's,  230 
carotid,  146 
cells  of,  1S6,  1S7 
ceruminous,  518 
ciliary,  499 
classification  of,  188 
coccygeal,  146 
compound,  187 
corpus  luteum,  332 
Cowper's,  319 
epithelium  of,  187 
excretory  ducts  of,  187 
dehiscent,  190 
development  of,  188 
ductless,  1S7,  190 
Ebner's,  199 
fundus,  219 
gastric,  218 

general  structure  of,  186 
genital,  348 
haemolymph,  141 
internal  secreting,  186 
interstitial  tissue  of,  188 
intraepithelial,  309 
kidney,  286 
lacrymal,  512 

large,  of  digestive  system,  242 
Lieberkiihn's,  228,  230 
lingual,  195 
Littre's,  321,  322 
liver,  253 
lobes  of,  1 88 
lobules,  iSS 
lymph,  147 
Mall's,  513 
mammary,  368 
Meibomian,  190,  514 
mixed,  194 
mucous,  194 

of  internal  secretion,  190 
of  the  oral  mucosa,  193 
ovary,  323 
pancreas,  247 
parathyreoids,  283 
parenchyma  of,  18S 
parotid,  243 
peptic,  219 
pineal,  490 
prehyoid,  283 
prostate,  317 
pyloric,  219,  220 


Glands,  racemose,  188 

reticular,  190 

saccular,  187,  190 
compound,  190 
simple,  190 

salivary,  242 

sebaceous,  355,  362 

secreting  portions  of,  187 

serous,  194 

simple,  187 

spleen,  158 

sublingual,  243 

submaxillary,  244 

sudoriferous,  189 

suprahyoid,  283 

suprarenal,  299 

sweat,  355 

tarsal,  514 

thymus,  153 

thyreoid,  280 

accessory,  283 

tonsils,  155 

tubular,  187,  188 
compound,  188 
simple  branched,  188 
simple  coiled,  188 
simple  straight,  188 

tubulo-alveolar,  187 

Tyson's,  321 

uterine,  337 
Glandulse  sudoriparse,  355 

vestibulares  majores,  346 
minores,  346 
Glandular  epithelium,  69,  186 
Glans  penis,  319 
Glenoid  ligaments,  181 
Glisson,  capsule  of,  253 
Globus  major,  304 

minor,  304 

pallidus,  472,  481 
Glomerulus  of  kidney,  288 

blood-vessels  of,  295 

olfactory,  531 
Glosso-pharyngeal    (IX.  nerve),    425, 

439,  493 

Glycerin  for  mounting  specimens,  20 
jelly,  20 

Glycogen  granules,  256 

Goblet  cells,  186 

Gold  chlorid  for  staining  connective- 
tissue  cells,  26 

Gold-size  for  glvcerin  mounts,  20 


.5.54 


INDEX. 


Golgi  cell.  Type  I.,  115,  117 

cell,  Type  II.,  115,  117,  399,  531 

method,  bichlorid,  33 
chrome-silver,  26 
Cox  modification  of,  ^^ 
formalin  bichromate,  ^;i 
mixed,  32 
rapid,  32 

silver,  for  nerve  tissue,  32 
slow,  for  nerve  tissue,  3  2 

muscle-tendon  organs  of,  390 

net,  122 

organs  of,  390 
Golgi-Mazzoni  corpuscles,  365 
GoU,  column  of,  408,  414 

nucleus  of,  414,  430 
Gowers'  tract,  416 
Graafian  follicles,  324 

antrum  of,  325 

corona  radiata,  326 

cumulus  ovigerus,  326 

development  of,  324,  349 

discus  proligerus,  326 

egg  nest,  325 

epithelium  of,  324 

follicular  cavity  of,  325 

germ  hill  of,  326 

liquor  folliculi,  325 

nerves  of,  333 

ovum  of,  325 

Pfltiger's  egg  cords,  324 

primitive  Graafian  follicle,  325 
ova,  324 

rupture  of,  329 

stratum  granulosum,  326 

technic  of,  335 

theca  folliculi,  326 

tunica  fibrosa,  326 

tunica  vasculosa,  327 
Graded  alcohols,  7 
Grandry,  corpuscles  of,  386 
Granule  theory  of  protoplasmic  struc- 
ture, 40 
Greater  omentum,  235 
Gray  matter,  377,  402 
Gray  rami  communicantes  381,  392 
Gray  reticular  formation,  419,  426 
Ground  bundles  of  spinal  cord,    399, 

4.3.3 
Griibler's  methylene  blue,  28,  35 

water-soluVjle  eosin,  28 
Gums,  mucfjus  membrane  of,    r93 


Gustatory  canal,  533 
Gyrus  dentatus,  477 
hippocampi,  477 

HABENUL.i',    468 

Haemalum,  Mayer's,  16 
Hasmatein,  15,  96 
Hasmatoidin,  crystals  of,  330 
Hasmatokonia,  95 
Hsematoxylin,  1 5 

and  eosin,  for  staining  double,  18 

and  picro-acid  fuchsin,  iq 

Delafield's,  15 

Gage's,  15 

Heidenhain's,  16 

Mallory's  stain,  26 

Weigert's  17,  29 
Haemoglobin,  96 
Haemolymph  nodes,  151 

blood  sinuses  of,  151 

blood-vessels  of,  153 

cells  of,  152 

eosinophiles,  152 
mast  cells,  152 
phagocytes,  152 

function  of,  153 

hilum  of,  151 

marrow-lymph,  152 

relation  of,  to  h^mphatic  system, 

153 
spleno-lymph,  152 
technic  of,  i  53 
Hair,  358 

arrector  pili  muscle  of  the,  361 
blood-vessels  of,  364 
bulb,  358 
cells,  521,  526 
cells  of  the,  360,  363 
connective-tissue  follicle  of,  360 
cortex  of,  359 
cortical  fibres  of,  359 
cuticle  of,  359 

development  of  the,  3 58,  366 
excretory  duct  of,  363 
eyelashes,  5  i  3 
follicle,  359 
germ,  363 
growth  of  the,  363 
hyaline  membrane,  3^)0 
inner  root  sheath,  359 
cuticle  of,  359 
Hcnle's  layer  of,  360 


IXDEX. 


Hair,  inner  root  sheath,  Huxle^^'s  layer 
of,  360 

lanugo,  the,  359 

layers  of  the,  359,  360 

lymphatics,  365 

medulla  of,  358 

nerves  of,  365 

outer  root  sheath,  360 

papilla  of,  358 

prickle  cells,  360 

root  of  the,  358 

root  sheath,  359 

sebaceous  glands  of  the,  362 

sebum  of  the,  363 

shaft  of,  358 

shedding  of  the,  363 

stratum  cylindricum,  360 

technic  of  the,  364 

vitreous  membrane,  360 
Halleri,  ductus  aberrans,  311 
Haller's  layer,  497 
Hamulus,  523 
Hardening,  8 

celloidin-embedded  specimens,  1 1 

clove-oil  celloidin-embedded  spec- 
imens,  12 
Hassal's  corpuscles,  154 
Haversian  canals,  165 

development  of,  178 

fringes,  181 

lamellae,  166 

spaces,  178 

systems,  167 

development  of,  178 
Hayem's  fluid,  57 
Head,  sympathetic  ganglia  of,  390 
Headgut,  193 

mouth,  193 

pharj'^nx,  2  i  2 

teeth,  200 

tongue,   196 
Hearing,  organ  of,  518:  see  Ear 
Heart,   140 

annuli  hbrosi,   14  i 

auricular  muscle,   140 

auriculo- ventricular  ring,   140 

blood-vessels  of,   141 

coronary  arteries  of,  141 

development  of,  143 

endocardium  of,  141 

epicardium  of,  141 

lymphatics  of,  142 


Heart  muscle,  106,  140;   see  also   In- 
voluntary striated  muscle 

myocardium  of,  140 

nerves  of,  142,  394 

technic  of,  142 

valves  of,  141 
Hecateromeres,  398 
Haeidenhain,  demilunes  of,  195 
Heidenhain's  haematoxylin,  16 
Heisterian  valve,  260 
Helicotrema,  523 
Heller's  plexus,  236 
Helweg,  tract  of,  418 
Hemispheres     of      cerebellum,      449, 

45  5 
Hendrickson,      concerning     coats     of 

liver  ducts,  260 
Henle's  laj^er,  360 

loop,  288,  290,  291 
sheath,  120,  382 
Hensen's  cells,  527 

line,  103 
Hepatic  artery,  254 
cells,  257 
cords,  257 
diverticula,  263 
duct,  255,  260 
Hermann,  showing  centrosome,  45 
Heteromeres,  398 
Hilum  of  liver,  253 
of  kidney,   286 
Hindbrain,  373,  429 
bulb,  429 

cerebellum,  374,  455 
medulla  oblongata,  374,  421; 
section    of,  through,    at    level    of 
junction   of   pons   and   cere- 
bellum, and  entrance  eighth 
nerve,  447 
through  roots  of  VI,  abducens, 

and  VII  facial  nerves,  450 
through  roots  of  V,  trigeminus 
nerve,  452 
His,  marginal  veil  of,  374 
myelospongium  of,  374 
spongioblasts  of,  374 
Histogenesis,  61 
Holmgren,   showing  trojihospongium. 

42 
Horizontal  cells,  482,  504 
Howship's  lacunae,  173 
Huxley's  la^-er,  3(10 


556 


INDEX. 


Hyaline  cartilage,  90 
Hyaloid  canal,  511 

membrane,  511 
Hyaloplasm,  40,  log 
Hydatid  of  Morgagni,  312 
Hj'drochloric  acid  for  decalcifying,  10 
Hyoglossal  fibres,  196 
Hypoblast,  56 
Hypoglossal    (XII    nerve),    435,    437, 

492 
Hyponychium,  358 
Hypophysis    cerebri,    489;    see    also 

Pituitary  body 
H3-pothalamus,  468,  477 

IxcisuRES    of    Schmidt-Lantermann, 

119 
Incremental  lines  of  Schreger,  202 
Indirect  cell  division,  48;  see  Mitosis 
Inferior     brachium     quadrigeminum, 

465 
cerebellar  peduncle;  see  Restiform 
body 
Infundibula,  274 
Injection,  22 

apparatus,  23 
double,  24 
separate  organs,  24 
whole  animals,  24 
Innervation  of  muscles,  388 
Interalveolar  connective  tissue,   277 
Interarticular  cartilages,  181 
Interbrain,  373,  468 

epithalamus,  374,  468 
hypothalamus,  374,  468 
thalamus,  374,  468 
Intercellular    bridges    of    epithelium, 
63,  66 
bridges  of  muscle  tissue,  102 
substance,  62 

of  connective  tissue,    76 
silver-nitrate  method  of  stain- 
ing, 26 
Intero-ceptors,  390 
Interfilar  mass,  4! 
Intermediate  cartilage,  179 
lamellae,  167 
neurones,  376 
Internal  arcuate  fibres,  438,  448 
Internal  capsule,  476 
Internal  ear,      520;      see      also     Ear, 
internal 


Internal  nuclei  of  cerebellum,  450,  455 
Internode,  119 
interradiary  plexus,  485 
Intersegmental    neurones,    378,    426, 
433.  435-  439.  447.  449.  452, 
454,  464 
Interstitial  lamellae,  167 

nucleus  of  Cajal,  417,  426,  476 
Intestine;    see    Small    intestine,    223; 

Large  intestine,  231 
Intestines,  development  of,  262 
Intima,  134 

coats  of,  134 

endothelial  layer  of,  134 

intermediary  layer  of,  134 

membrana  elastica  interna,  135 

of  arteries,  134 

of  lymph  vessels,  143 

of  veins,  138 
Intracartilaginous   bones,  growth   of, 
179 

ossification,    175 
Intracellular  canals,  42 
Intrafascicular  connective  tissue,  184, 

382 
Intramembranous  ossification,  172 
Intranuclear  network  of  typical  cell, 

44 
Involuntary  striated  muscle   (heart), 
106 
Cohnheim's  field,  106 
development  of,  in  pig  (McCal- 

lum),  109 
McCallum's  views,  106,  109 
membrane  of  Krause,  106 
muscle  columns  of  Kolliker,  106 
nerves  of,  394 
sarcoplasm  of,  106 
technic  of,  1 10 
smooth  muscle,  10  r 

intercellular  bridges  of,  102 
Iodine,  to  remove  mercury,  9 
Iris,  the,  500 

greater  arterial  circle,  5  i  r 
layers  of  the,  500 
lesser  arterial  circle,  511 
muscles  of  the,  50 1 
pigmentation  of,  500 
vitreous  membrane,  50  r 
Irritability  of  cells,  46 
Islands,  blood,  99,  142 
of  Langerhans,  250 


INDEX. 


Isolated  smooth  muscle  cells,  loi 

technic  of,  no 
Isotropic  line,  103 

substance,  103 
Isthmus,  374,  462 

section  through,    at   exit   of   IV, 
trochlearis,  nerve,  462 
at  level  of  optic  chiasma,  472 
Iter,  374,  462,  464 

Tenner's  blood  stain,  28 
Joint  capsule,  181 

stratum  fibrosum,  181 
synoviale,  181 

synovial  membrane,  181 
Joints,  180;  see  Articulations 
Jugular  ganglion  of  X,  425 
Juxta-restiform  body,  449 

Karyolysis,  354 

Karyoplasm,  41 

Karyosomes,  44 

Katabolism,  45 

Keratin,  354 

Keratohyaline  granules,  354,  358 

Kidney,  the,  286 

arteriae  arciformes,  294 
rectse,  296 

blood-vessels  of,  293 

Bowman's  capsule  of,  290 

capillaries  of,  295 

columns  of  Bertini,  288 

convoluted  tubules  of,  288 

cortex  of,  286 

cortical  pyramids  of,  288 

development  of,  301,  346 

duct  of  Bellini,  289 

epithelium  of,  292 

glomerulus  of,  288 

Henle's  loop,  291 

interlobar  arteries  of,  293 

hilum  of,  286 

labyrinths  of,  288 

lobulated,  286 

location  of  tubules  in,  292 

lymphatics  of,  296 

main  excretory  duct  of,  297 

Malpighian  body,  288 
pyramid,  288 

medulla  of,  286 

niedullary  (or  Malpighian)  pyra- 
mid, 288 


Kidney,  medullary  rays,  288 

nerves  of,  296 

papillas  of,  287 

pelvis  of,  287,  297 

pyramids  of  Ferrein,  288 

renal  artery,  286 
corpuscle,  288 
vein,  286 

renculi  or  lobes  of,  286 

septa  renis,  288 

single  lobe  of,  286 

stellate  veins  of  Verheyn,  296 

technic  of,  302 

ureter,  286,  297 

uriniferous  tubule,   288;  see  also 
Uriniferous  tubule 
Kidney-pelvis,  297 

blood-vessels  of,  297 

calyces  of,  297 

coats  of,  297 

development  of,  346 

lymphatics  of,  297 

nerves  of,  297 

technic  of,  302 
KoUiker,  muscle  columns  of,  103 

showing  Golgi  cell  type  II,  116 
spleen  cells,  161 
Krause,  ellipsoid,  503 

end-bulbs,  200,  321,  365,  512 

line  of,  103 
Kupffer,  cells  of,  258 

Labia   minora,    sebaceous   glands   of, 

355 
Labyrinth,  membranous,  520 

osseous,  520 
Lacrymal  apparatus,  512 
canal,  513 
gland,  512 

blood-vessels  of,  513 
excretory  ducts  of,  513 
lyinphatics  of,  513 
nerves  of,  513 
technic  for,  518 
nasal  duct  of,  513 
sac,  513 
Lacteals,  240 
Lacunae,  89,  93 

origin  of,  173 
Lamellae,  circuinferential,   1(17 
Haversian,  166 
intermediate,  167 


558 


INDEX. 


Lamellae,  interstitial,  167 

of  bone  tissue,  93 
Lamina,  bony  spiral,  523 

citrea,  497 

cribrosa,  494,  506 

fusca,  494 

reticularis,  527 

suprachorioidea,  497 
Laminse  of  cerebellum,  455 
Langerhans,  cell  islands  of,  250 

centro-acinar  cells  of,  249 

centro-tubular  cells  of,  249 
Lanugo  hairs,  359 
Large  intestine,  231 

Auerbach's  plexus,  232,  238 

blood-vessels,  326 

coats  of,  231 

development  of,  262 

gland  tubules,  232 

lineae  coli,  232 

lymphatics,  237 

nerves,  238 

plexus  of  Meissner,  232,  238 
mj'entericus,  238 

technic  of,  241 
Larynx,  the,  266 

blood-vessels  of,  268 

cartilages  of,  266 
arytenoid,  266 
cricoid,  266 
epiglottis,  266 
Santorini's,  266 
thyroid,  266 
Wrisburg's,  266 

cells  of,  266 

develojjment  of,  280 

epithelium  of,  266 

lymphatics,  268 

nerves,  268 

perichondrium,  266 

technic,  269 
Lateral  lemniscus,  441,  449,  450,  462 
Law  of  Wallerian  degeneration,  j  22 
Lemniscus,  378,  381 

lateral,  441,  449,  450,  462 

medial,  4/4,   426,   435,   43^'.   44°, 
442,  446,  451,  452,  453 
Lenhossck,  concerning  ciliated  ejjithe- 

lium,  68 
Lens,  510 
Lenticular  nucleus,  477,  478 

canal  of  Petti t,  5  '  1 


Lenticular  capsule,  510 

epithelium,  510 

fibres,  510 

hyaloid  membrane,  511 

suspensory  ligament,  510 

zonula  ciliaris,  510 

zonule  of  Zinn,  510 
Leopold,  concerning  pregnant  uterus, 

340 
Leucocytes,  96 

lymphocytes,  96 

migratory,  226 

mononuclear,  97 

of  milk,  370 

polymorphonuclear,  97 

polynuclear,  97 

transitional,  97 
Lewis,    concerning    shape    of    blood- 
cells,  95 
Lieberkiihn,  crypts  of,  228,  230 

glands  of,  228 
Ligament,  circular  dentoid,  205 

glenoid,  180 

spiral,  523 

structure  of,  78 

suspensory,  510 
Ligamentum  nuchse,  79 

pectinatum,  500 
Lineae  coli,  232 
Line  of  Gennari,  488 
Lines  of  Retzius,  204 
Lingual  glands,  195 

tonsils,  157 
Lingualis,      genio-glossus     fibres     of, 
196 

hyoglossus  fibres  of,   196 

longitudinal  fibres  of ,  197 

styloglossus  fibres  of,  197 

transverse  fibres  of,  196 
Linin,  44 

Lipoid  granules,  299 
Licjuor  ferri  sesquichlorati,  26 

folliculi,  325 
Lissauer,  zone  of,  397,  403 
Littrc',  glands  of,  321,  322 
Liver,  the,  253 

blood  supply  of,  254 

capillary  network,  255 

capsule  of  Glisson,  253 

cells  of,  256 

of  Kupffer,  258 

central  vein  of,  255 


INDEX. 


559 


Liver,    compared    with    other     com- 
pound tubular  glands,  2 58 
connective  tissue,  253 
cords  of  liver  cells,  257 
development  of,  263 
ducts,  260 

common,  260 

cj'stic,  260 

hepatic,  260 
glycogen  granules,  256 
Heist erian  valve,  260 
hepatic  artery,  254 

cords,  257 

duct,  255 
hilum,  2^^ 
intralobular     secreting     tubules, 

255 
lobes  of,  253 
lobules,  253 
lymphatics,  260 
main  ducts,  260 
nerves,  260 
portal  canal,  255 

vein,  254 
radiate  fibres,  258 
reticulum,  258 
septa,  253 

sublobular  vein,  255 
technic  of,  261 
tubules  of,  257 
Lobulated  kidney,  286 
Lowenthal,  anterior  marginal   bundle 

of,  418 
Longitudinal  cleavage,  5  i 

fasciculus,  439,  447,  454,  4'H,  4^1 
Loop  of  Henle,  2gi 
Loose  (areolar)  connective  tissue,  77 
Lumbar  enlargement  of  spinal  cord, 
396 
segments  of  cord,  396 
Lungs,  the,  273 
air  cells,  274 
sacs,  274 
vesicles.  274 
alveolar  ducts,  274,  275 

sacs,  274,  275 
alveoli  of,  274 
atria  of,  274 
blood-vessels  of,   277 
bronchial  artery,   277 

system,  277 
capsule  of,  273 


Lungs,  cells  of,  276 

development  of,  279 
epithelium  of,   275 
foetal  cells  of,  275,  276 
infundibula  of,  274 
interalveolar  connective  tissue  of, 

277 
lobes  of,  273 
lobules  of,  273 
lymphatics  of,  279 
Miller's  subdivisions,  274 
nerves  of,  279 
parietal  pleura,  273 
pulmonary  artery,  277,  279 

lobule,  273,  278 

pleura  of,  273 
respiratory  bronchi,  274 

cells,  276 

epithelium,  275 
septa  of,  273 
technic  of,  280 
terminal  bronchi  of,  274 
vestibula  of,  274 
Lunula,  358 
Lutein  cells,  329 
Luteum,  corpus,    329 
Luys,  nucleus  of,  469 
Lymph,  63 

capillaries,  143 

glands,  147;  see  LympJi  nodes 

nodes,  147 

blood-vessels  of,  150 

capsule  of,  147 

chains  of,  147 

connective  tissue  of,   147 

cords  of,  14S 

cortex  of,  148 

germinal  centre  of,  148 

lymphatics  of,  150 

medulla  of,  148 

nerves  of,  150 

nodules  of,  148 

reticular  connective  tissue  of, 
149 

sinuses  of,  14S 

technic  of,  150 
nodule,  84,  148 

germinal  centre  of,  147 
paths  of  the  eye,  5 1  2 
spaces,  144 

pericellular,  144 
vessel  system,  143 


560 


INDEX. 


Lymph  vessel  system,  capillaries  of,  144 
developm.ent  of,  145 
lymph  capillaries,  144 

spaces,  144 
relation     of,     to     hsemolymph 

node,  153 
technic  of,  144 
vessels,  coats  of,  143 
structure  of,  143 
Lj-mphatic  organs,  147 

development  of,  145 
hsemolymph  nodes,  151 
lymph  nodes,  147 
spleen,  158 

technic  of,  150,  153,  155,  158 
thymus,  153 
tonsils,  155 
tissue,  84,  148 
Lymphocytes,  85,  96 
Lymphoid  cells,  84,  148 
tissue,  149 

Macerating  fluids,  4 
Maceration,  4 
Macula  acustica,  521 
lutea,  505 

fovea  centralis,  505 
Male  genital  organs,  303 

pronucleus,  53 
Mall,  glands  of,  513 

concerning  development  of  fibril- 
lar connective  tissue,  78 
concerning  splenic  pulp,  162 
Mallory's  aniline  blue  stain  for  con- 
nective tissue,  28 
haematoxylin  stain,  27 
phosphomolybdic      acid      haema- 
toxylin stain  for  connective 
tissue,  27 
phosphotungstic  acid  haematoxy- 
lin stain  for  connective  tis- 
sue, 27 
Maljjighian  bodies,  159 

body  of  kidney,  288,  290 

development  of,  288,  347 
];yramid,  288;  see  Kidney 
Mamillo-thalamic  tract,  469 
Mammary  gland,  368 
active,  368 
alveoli  of  active,  369 
ampulla  of,  368 
blood-vessels  of.  370 


Mammary  gland,  cells  of,  369 

colostrum  corpuscles,  370 

development  of,  371 

ducts  of,  368 
of  nipple,  368 

inactive,  368 

interlobar  septa  of,  368 

interlobular  septa  of,  368 

lobular  ducts  of,  368 

lymphatics  of,  370 

milk,  370 

nerves  of,  370 

secretion  of,  369 

structure  of,  368 

technic  of,  371 
Mantle  fibres,  48 

Marchi's     method     for    staining    de- 
generating nerves,  3 1 

Busch's  modification  of,  31 
Marginal  bundle  of  Lowenthal,  418 

veil  of  His,  374 
Marrow,  168;  see  Bone  marrow 

lymph  nodes,  152 
Martinotti,  cells  of,  483 
Mast  cells,  75,  98 
Matrix  of  nail,  356 
Maturation,  52 

of  ovum,  52,  328 

of  spermatozoon,  52 
Mayer's  hsemalum,  16 
McCallum,   concerning  heart   muscle, 

106,  109 
Media  of  arteries,  135 

of  lymph  vessels,  143 

of  veins,  138 
Medial  column,  357 

eminence,  430 
Median  center  of  Luys,  477 

lemniscus,  414,  426,  435 

raphe,  381,  438 

septum,  posterior,  401 
Mediastinum  testis,  303 
Medulla  oblongata,  429 

accessory  olivary  nucleus,  438 
olives,  438 

afferent  cerebellar  neurones,  438, 

447 
roots,  433,  435,  23S,  439 

secondary    tracts     of,     433, 

435.  438,  439 
terminal  nuclei  of,  433,  435, 

438,  439 


INDEX. 


501 


Medulla  oblongata,  ala  cinerea,  437 

anterior  fissure,  430 

ground    bundles,  see    Interseg- 
mental neurones 
pyramid,  430,  447 

arciform    (arcuate)    nucleus,  378, 
381,  384 

arcuate  fibres,  435,  438 

auditory  nerve,  441 

central  canal,  430 

gelatinous  substance,  437 
gray  matter,  431,  433,  437 
tegmental  tract,  439,  447 

cerebellar  peduncles,  447 

cerebello-olivary  fibres,  438,  439, 

447 
chorioid  plexus,  437 
clavia,  430 
cochlear  nerve,  439,  441. 

nuclei,  441 
column  of  Burdach,  430,  435 

of  Goll,  430,  435 
compared  with  spinal  cord,  430 
corpus  restiforme,  436,  438,  449 
crossed  pyramidal  tract,  416,  433 
cranial  nerves  of,  429,  430 
decussation  of  fillet,  435 

of  pyramids,  431 
Deiter's  nucleus,  435,  447 

tract,  435 
descending   root    of    fifth    nerve, 

430 
or  spinal  root  of  vestibular  por- 
tion of  eighth  nerve,  439 
suprasegmental  paths,  433 
tract    from    Deiter's    nucleus, 

435.  439.  447 
from   the   vestibular   nuclei, 
441 
development  of,  374 
direct  cerebellar  tract,  433 
direct  pyramidal  tract,  433 
funiculus,  433 
horns,  431 
nucleus  of  ninth  cranial  nerve, 

439.  440 
nucleus    of   tenth    nerve,    430, 

43  5-  437 
efferent       peripheral       neurones, 

431.  435.  437.  439 
suprasegmental  neurones,  433, 

437.  439.  447 
36 


Medulla  oblongata,   eminentia  hypo- 
glossi,  437 
spino-cerebellar  tract,  433,  435 
external  arcuate  fibres,  435,  438, 

447 
fasciculus  cuneatus,  433 

gracilis,  433 
fillet    or    medial    lemniscus,  414, 
426,  435,  436,  440,  442,  446, 

447.  451 
formatio  reticularis,  439 
fourth  ventricle,  430,  437 
funiculus  cuneatus,  435 

gracilis,  435 
gelatinous  substance  of  Rolando, 

433.  437 
general  structure  of,  429 
genu  facialis,  43 1 
Gowers'  tract,  see  Ventral  spino- 
cerebellar 
gray  reticular  formation,  431 
internal  arcuate  fibres  of,  438 
intersegmental    neurones,    431, 

435.  439.  447 
lateral  fillet,  441 

lemniscus,  441 
longitudinal  fasciculus,  439 
median  lemniscus,  414,  426,  435, 

436,  440,  442,  446,  447,  451 
longitudinal     fasciculus,      439, 

447 

raphe,  436,  438 
nuclei  arcuati,  438,  447 

of  the  floor  of  the  ventricle,  430 

laterales,  438 

of  the  thalamus,  469 

of  posterior  columns,  430,  435 
nucleus,  abducentis,  431 

accessory  cuneate,  435 

alse  cinereas,  435,  437 

ambiguus,  437,  439 

commissuralis,  435 

cuneatus,  430,  435 

gracilis,  430,  435 

hypoglossi,  430,  435 

of  acoustic  nerve,  431,  430,  441 

of    the    column    of     Burdach, 

430.  435 
of  the  column  of  Goll,  430,  435 
of  the  fifth  spinal  nerve,  435 
of    origin    of    eleventh    cranial 

(spinal-accessory)  nerve,  43 1 


.562 


INDEX. 


Medulla  oblongata,  nucleus  of  origin 
of  twelfth  cranial  (liypoglos- 
sal)  nerve,  435,  437 
of  vagus  nerve,  430,  437 
olives,  437,  447 
olivary  nucleus,  438,  439 
olivo-cerebellar  fibres,   438,   439, 

44  7 
pallio-spinal  tract,  433 
peduncles  of,  447 
plexus  chorioideus,  431 
pons  Varolii,  447 
posterior  columns  of,  435 

longitudinal  fasciculus,  439 

septum,  430 
predorsal  tract,  439 
pyramidal  decussation,  433 

tracts,  433,  437 
raphe,  436,  438 

restiform body,  430,  436,  438,  439 
reticular  formation,  431,  433,  435 

437.  439-  447 
reticulo-spinal  tract,  433 
root  fibres  of  spinal  V.,  433 

and  nucleus  of  origin  of  sixth 

{abdiicens)  cranial  nerve,  447, 

448,  450 
and  nucleus  of  origin  of  seventh 

{facial)  cranial  nerve,  439 
and  nuclei  of  eighth  {auditory) 

cranial  nerve,  441 
of      ninth      {glosso- pharyngeal) 

and    tenth     {vagus)     cranial 

nerves,  439 
of  eleventh      {spinal-accessory) 

cranial  nerve,  43  i 
of    twelfth     (hypoglossal)     cra- 
nial nerve,  435,  437 
rubro-s]jinal  tract,  435,  439,  447 
secondary  cochlear  tract,  441 
vestibular  tract,  44  i 
sensory  tract  of  fifth  nerve,  433 
section    through    decussation    of 

fillet,  435 
through    entrance   of   cochlear 

branch  of  eighth,  439 
through  lower  part  of  inferior 

olivary  nucleus,  437 
through      middle      of      olivary 

nucleus,  439 
through     pyramiflal     decussa- 
tion, 43  I 


Medulla    oblongata,  section    through 
sensory  decussation,  435 
sensory  decussation  of,  435 
and  motor  nuclei  of  the 
fifth  nerve,  452 
solitary  fasciculus,  438,  439 
spinal   (descending)   root  of  fifth 
cranial  nerve,  432,  433,  435, 
436,  438.  440,  441,  448,  451. 
452 
v.,  435 
spino-tectal  tract,  433,  437,  439, 

447 
-thalamic  tract,  435 
striae  meduUares,  441 
technic  of,  421,  431 
tecto-spinal  tract,  433,  437,  439 
tegmentum,  447 

terrainal  nucleus  of  the  descend- 
ing  (sensory)   root  fibres   of 
the  fifth  nerve,  433 
tract     of     Gowers,     see     Ventral 
spino-cerebellar 
from     interstitial     nucleus     of 

Cajal,  433,  435 
of  Helweg,   418,   432,   434 
of  Lowenthal,  418 
tractus  spinalis  trigemini,  433 
trapezius,  441 
tuberculum  cinereum,  430 
ventral     spino-cerebellar     tract, 

433 

vestibular  nerve,  441 

vestibulo-spinal  tract,  433 

Von  Monakow's  bundle,  417 
Medullary  pyramid  (Malpighian),  288 

rays,  288 

sheath,   117,   119 
superior,  462 
Medullated     nerve     fibres,     Weigerts' 

stain  for,  29 
Megalocytes,  j  6  1 
Meibomian  glands,   190,  514 
Meissner,  corpuscles  of,  321,  365,  387 

plexus  of,   215,   222,   230,   238 
Membrana  chorii,  341 

elastica  externa,  137 
interna,  135 

limitans  olfactoria,  265 

preformativa,  2  i  1 

propria,  63 

tectoria,  527 


INDEX. 


563 


Membrane,  basal,  63 

cuticular,  209 

mucous,  iQi 

of  Bowman,  495 

of  Desceniet,  496 

of  Krause,  106 

of  Reissner,  524 

peridental,  205 

serous,  144 

synovial,  iSi 
Membranes  of  brain  and  cord,  378 
Membranous  cochlea,  523 

labyrinth,  520 

spiral  lamina,  523 
ligament,  523 
Meninges,  37S 
Menstrualis,  decidua,  339 
Menstruating  uterus,  338 
Menstruation,  339 
Mercuric  chlorid  as  a  fixative,  7 
Merkel's  corpuscles,  386 
Mesencephalic    root    of    fifth    (trigem- 
inus) cranial  nerve,  452 
Mesencephalon,  373 
Mesentery,  235 
Mesoappendix,  233 
Mesoblast,  56 
Mesoderm,  56 

tissue  derivations  from,   61,   262, 
279 
Mesonephros,  334 

derivations  from,  312,  334 
Mesothelium,  62,  70 
Metabolism  of  cells,  45 
Metanephroi,  346 
Metaphase,  5  i 
Metaplasm,  42 

Methods  for  studying  fibre  tracts  of 
the  cord,  408 
atroph}'-,  413 

axonal  degeneration,  408 
comparative  anatomy,  413 
myelogenetic,  408 
physiology,  413 
secondary  degeneration,  40S 
Methyl  blue,  i  7 

green,  17 

violet,  17 
Methjdene  blue,  35 
Meynert,  decussation  of,  4O7 

librae  proprias  of,  479 

radiations  of,  4S5 


Micron,  14 
Microsomes,  40 
Microtome,  14 
Midbrain,  373,  464 

anterior     corpora     quadrigemina 

of,  464,  465,  467 
aqueductus  Sylvii,  464 
basis  pedunculi,  464,  465 
brachia  conjunctiva,  450 
cerebral  peduncles,  464,  465 
coUiculi,  374 

corpora  quadrigemina,  374,  464 
cranial  nerves  III.  and  IV.,  464 
crura  cerebri,  465 
decussation  of  Forel,  467 

of  Meynert,  467 
Edinger-Westphal  nucleus,  465 
fourth  cranial  nerve,  465 
geniculate  bodies  of,  465 
inferior     brachium     quadrigemi- 
num,  465 
colliculi,  464 
internal  arcuate  fibres,  467 
iter,  464 

lateral  lemniscus,  465,  466 
mesencephalic  root  of  fifth  nerve, 

465 
optic  nerve,  467 
pes  pedunculi,  464,  465 
posterior  corpora  quadrigemina, 
464 
longitudinal  fasciculus,  467 
red  nucleus  of,  467 
reticular  formation,  467 
root  fibres  and  nucleus  of  origin 
of  third  (oculomotor)   cranial 
nerve,  465 
through   exit   of   third    (oculo- 
motor) cranial  nerve,  465 
spino-tectal  tract,  467 
substantia  nigra,  464,  4(1$,  467 
superior  cerebellar  peduncles  of, 
467 
colliculi,  464,  465 
tegmentum,  374,  464 
Middle  ear,  519;  see  Ear.  middle 
Midgut,  223 

small  intestine,  223 
Migratory  leucocytes,  226 
Milk,  370 

cells  of,  370 

colostrum  corpuscles  of,  370 


564 


INDEX. 


Milk  teeth,  206,  208 
Miller"  s  theory  of  lung  subdivisions ,  274 
Minot,    concerning   endothelium    and 
mesothelium,  70 
concerning  the  pregnant  uterus, 

340 
Miton,  40 
Mitosis,  48 

anaphase,  51 

metaphase,  5 1 

method     of     demonstrating     by 
Flemming's  fluid,  7 

prophase,  48 

technic  for,  58 

telophase,  5  i 
Mitotic  figure,  5  i 
Mitral  cells,  530 
Modiolus,  522 
Monaster,  49,  51 
Mononuclear  leucocytes,  97 
Monosynaptic  arc,  420 
Mordanting,  29 
Morgagni,  hydatid  of,  312 
Motion  of  cells,  46 
Motor  cells  of  anterior  horns,  380 

decussation,  43  i 

end  plate,  395 

nuclei,  395 

path  to  cranial  nerves,  454 

peripheral  nerves,  380 

precentral  area,  416,  479,  488 
Mounting,  20 

celloidin  specimens,  21 

in  balsam,  2  i 

in  glycerin,  20 

paraffin  sections,  2  i 
Mouth,  the,  193 

blood-vessels  of,  195 

end  bulbs  in  mucous  membrane, 

387 

glands  of,  193 

lymphatics  of,  195 

mucous  membrane  of,  193 

nerves  of,  195,  387 

technic  of,  196 
Mucin,  82,  J94 
Mucous  glands,  194 

membranes,  191 

basement  membrane  of,  J91 
end  bulbs  in,  387 
general  structure  of,   r  9  j 
membrana  propria,  191 


Mucous  membranes,  muscularis  mu- 
cosse,  191 
nerves  of,  387 
of  alimentary  tract,  192 
stroma  of,  191 
surface  epithelium,  191 
tactile  cells  of,  386 
corpuscles  of,  386 
tissue,  81 

tunica  propria  of,  191 
Mucus,  186,  194 
Miiller,  cells  of,  504,  505 

circular  muscle  of,  500 
fibres  of,  504 
MuUer's  fluid,  6 
Miillerian  ducts,  318 
Multipolar  nerve  cells,  112,  384 
Muscle,  arrector  pili,  361 
auricular,  140 
cells,  1 01 
ciliary,  499 

circular,  of  Muller,  490 
columns  of  Kolliker,  103 
discs,  103 
fibrillse,  103 
nuclei,  102 
of  sweat  glands,  3 68 
spindles,  or  neuro- muscular  bun- 
dles, 388 
tendon  junction,  184 
organs  of  Golgi  in,  388 
peripheral  nerve  terminations 
in,  388 
tissue,  10 1 

classification  of,  10 1 
development  of,  loS 
heart,  106 

histogenesis,  107 
intercellular  bridges  of,  102 
involuntary  smooth,  loi 

striated,  106 
technic  of,  109 
voluntary  striated,    102 
anisotropic  substance,  103 
Cohnheim's  fields,  103 
end  bulbs  of,  388 
ergastoplasm,  102 
Hensen's  line,  103 
isotropic  substance,  103 
Krause's  line,  103 
muscle  columns  of  Kolliker, 
103 


INDEX. 


ofio 


Muscle     tissue,     voluntary     striated, 
muscle  discs,  103 
nuclei,  102 
spindles,  388 
substance,  102 
nerves  of,  388 
Pacinian  corpuscles  of,  388 
Rollett's  theory,  104 
Ruffini's  theory  of  nerve  ter- 
minations in,  388 
sarcolemma,  102 
sarcous  element  of  Bowman, 

103 
technic  of,  no 
terminations  in,  388 
annular,  388 
arborescent,  388 
spiral,  388 
ultimate  fibrillae,  103 
white  and  red  fibres,  105 
Muscles,  voluntary,  183 
capsule  of,  183 
endomysium,  184 
epimysium,  183 
fascicles  of,  183 
growth  of,  184 
intrafascicular  connective  tissue 

of,  I  84 
perifascicular  sheath,  184 
perimysium,  184 
Muscular  system,  183 
blood-vessels  of,  185 
bursas  of,  184 
lymphatics  of,  185 
nerves  of,  185 
technic  of,  185 
tendons  of,  78,  184 
tendon  sheaths  of,  184 
voluntary  muscle,  183 
Muscularis  mucosse  of  mucous  mem- 
branes, 191 
Musculature  of  intestine,  102 
Myelin,  iiq 

Myeloarchitecture,  488 
Myelocytes,  16S 

Myelogenetic    method    for    determin- 
ing fibre  tracts  of  cord,  408 
Myeloplaxes,  i6q 
Myelospongium  of  His,  3  74 
Myentericus,  plexus,  23 8 
Myoblast,  loS,  185 
Myocardiuni,  140 
primitive,  143 


Myotome,  108 
Myxoedema,  282 


Nabothi,  ovula,  338 
Nails,  the,  356 

cells  of  the,  358 

development  of,  366 

eponychium  of,  358 

growth  of,  358 

hyponychium,  358 

keratohyalin  of,  358 

lunula  of,  358 

matrix  of,  356 

prickle  cells  of,  358 

structure  of,  356 

technic  of,  358 
Nail-bed,  356 

groove,  356 

wall,  356 
Nares,  264 

accessory  nasal  sinuses,   264 

cells  of,  265 
basal,  265 
olfactory,  265 
sustentacular,  265 

development  of,  280 

glands  of  Bowman,  265 

membrana     limitans     olfactoria, 

265 
stroma  of,  265 
structure  of,  264 

olfactory  region,  264 
respiratory  region,  264 
vestibular  region,  264 
technic  of,  269 
zone  of  oval  nuclei,  265 
of  round  nuclei,  265 
Nasal  duct,  513 
Nemileff",  showing  amitosis,  48 

showing  meduUated  nerve  fibre, 
120 
Neopallium,  477,  478,  479 
bundles  of,  479 
efterent  connections  of,  479 
Nerve  cells,  in;  see  also  Neurone 
amacrine,  504 
amphicytes,  383 
anterior  horn,  398 
association,  483 
basket,  195,  457 
Betz',  47q,  482,  4S4 
bipolar,  112,  384 


566 


INDEX. 


Xerve  cells,  brush,  531 
Cajal's,  482 
caryochromes,  114 
cerebro-spinal  ganglia,  382 
column,  396,  398 
cone-bipolar,  503 
cone-visual,  503 
efferent  projection,  483 
ependymal,  374 
extrinsic,  396 
ganglion,  382,  385,  397 
giant,  of  Betz,  482 
glia,  125 
Golgi,  Type  I,  115,  117 

Type  II,  116,  117,   396,   399 
hecateromeric,  398 
heteromeric,  398 
horizontal,  482,   503 
in  gray  matter  of  cord,  396 
intrinsic,  396 
inverted  pyramidal,  482 
large  granule  cells,  458 
Martinotti's,  482,  483 
mitral,  530 
mossy,  126, 
motor,   of    the    anterior    horn, 

398 

Miiller's,  504 

multipolar,  112,  384 

neuroblasts,  iii,  126,  374 

neuroglia,  374,  462,  482 

of  motor  area  of  cerebral   cor- 
tex, 483 

outside  the  spinal  cord,  397 

peripheral  motor,  395 
sensory,  382 

]jolymorphous,  482 

Purkinje,  456 

pyramidal,  48  r 
inverted,  482 

rod-bipolar,  503 

rod- visual,  503 

root,  396 

small  granule,  458 

somatochromes,  1  (4 

spider,  126 

spinal  ganglion,  390,  397 

spongioblasts,  374 

stellate,  457,  482 

sympathetic  ganglion,  390 

tautomeric,  398 

nnijKjlar,   f  i  2,  383 


Nerve    endings,    385;    see    Peripheral 

nerve  terminations 
fibres,  113 
afferent,  376 
association,  478 
climbing,  460 
commissural,  478 
cone,  503 

deep  tangential,  485 
felt  works  of,  394 
layer  of,  of  retina,  504 
medullated,  117 

of  cerebellum,  461 

methods  of  staining,  29 
mossy,  460 

motor  end  plates  of,  395 
non-medullated,  117 
of  Bergmann,  462 
origin   of,   of   white   matter   of 

cord,  396 
pallial,  478 
pallio-pontile,  464 
pallio-tectal,  479 
pallio-thalamic,  479 
parallel,  of  the  cerebellum,  458 
perpendicular  pontile,  454 
projection,  478 
rod  and  cone,  503 
superficial  tangential,  488 
terminations,  385 
motor,  395 
sensory,  385 
tissue,  1 1 1 

Golgi  methods  of  staining,    32 
neuroglia,  125 
neurone,   1 1 1 

axone,  116 

cell  body,  1 1 1 

dendrites,  1 16 

protoplasmic  processes,  116 
technic  for,  127 
Nerves,  cranial,  table  of,  492 

motor    and    sensory    nuclei    of, 

377 

III  (oculomotor),  464,  465 
oculomotor  nucleus,  465 

root     fibres     and     nucleus     of 
origin  of  third,  450,  465,  470 

IV  (trochlearis),  462,  464 
root     fibres     and     nucleus     of 

origin  of  fourth,  462,  465 

V  (trigeminus),  425 


INDEX. 


567 


Nerves,    cranial,    mesencephalic   root 

of  fifth,  452,  462,  465 
motor  nucleus  of  fifth,  452 
semilunar  ganglion  of  fifth,  425 
sensory  nucleus  of  fifth,  452 

and     motor     root     fibres   of 

fifth,  452 
spinal  root  of  fifth,   432,   433, 

435,  436,  438,  440,  441,  448, 

449,  450,  451,  452 

VI  (abducens),  448 

nucleus     of     origin     of     sixth, 
447.  448,  450 
abducentis,  450 
root  fibres  of  sixth,   447,  448, 

450 

VII  (facial),  425 
ganglion  geniculate,  425 
nucleus  facialis,  447 

of   origin   of   seventh,  447 
root  fibres  of  seventh,  439,  447 

VIII  (auditory),  425,  431,  441 
cochlear     branch     of     eighth, 

441,  439,  443 
ganglion  of  Scarpa,  425,  441 

spirale,  425,  441 
nuclei  of  eighth,  438,  441,  450 

Deiter's,  448,  449 

von  Bechterew's,  448,  454 
root  fibres  of  eighth,  441 
vestibular    branch    of    eighth, 

425,  438,  441,  445,  448 

IX  (glosso-pharyngeal) ,    425, 

439 
descending     or     sensory     root 

fibres  of  the  ninth,  439 
dorsal   nucleus   of   ninth,    439, 

440 
motor  nucleus  of  ninth,  439 
root  fibres  of  ninth,  438,  439 

X  (vagus),  425,  437 
descending     or     sensory     root 

fibres  of  tenth,  437,  43S 
dorsal   nucleus  of    tenth,  435, 

437 
ganglion  jugular,  425 

nodose,  425 
motor  nucleus  of  tenth,  438 
root  fibres  of  tenth,  437,  439 

XI  (spinal  accessory),  43  i 
nucleus  of  origin  of  eleventh, 

431 


Nerves,  cranial,  root  fibres  of  eleventh, 
43  i 
XII  (hypoglossal),  435,  436,437 
nucleus    of    origin    of   twelfth, 

435-  436,  437 
root  fibres  of  twelfth,  435,  437 
mixed  spinal,  380,  381 
olfactory,  477 
peripheral,  380 

spinal,  anterior,  motor  or  efferent 
roots  of,  395 
sensory,    or    afferent    portions, 
382 
Nervous  system,  the,  373 
cerebro-spinal,  373 
development  of,  373 
general  structure  of,  3  73 
sympathetic,  373 
central,  373 

afferent    peripheral    neurones, 

382 
brain,  424 

cerebro-spinal  ganglia,  382 
cranial  nerves,  425,  492 
development  of,  373 
efferent      peripheral      cerebro- 
spinal neurones,  395 
general  structure  of,  373 
histological     development     of, 

373 
membranes  of  brain  and  cord, 

378 
segmental  part,  377,  425 
spinal  cord,  396 

nerves,  380,  492 
suprasegmental  part,  377,  427 
cerebro-spinal,  373 

central  nervous  system,  373 
peripheral  portion,  373,  380 
sy 111  pathetic,  373 

development  of,  375 
ganglia,  373,  390 
sympathetic  nerves,  373,  31)0 
Neumann's  dental  sheath,  203 
Neural  arc,  377,  420 
cerebellar,  42  i 
cerebral,  42  i 
disynaptic,  42  i 
mono-synaptic,  420 
])allial,  42  I 

three-neurone,  spinal,  421,  435, 
452 


568 


INDEX. 


Neural  arc,  two-neurone,  spinal,  420 

fold,  373 

groove,  373 

plate,  373 

tube,  373 
cells  of,  374 

ependymal  cells  of,  374 
marginal  veil  of  His,  374 
myelospongium  of  His,  374 
neuroblasts,  374 
neuroglia  cells  of,  374 
spongioblasts  of  His,  374 
Neuraxone,  1 1 1 
Neurilemma,  117,  119 

and  axolemina,  relation  of,   120 

-cells,  375 
Neurite,  1 1 1 
Neuro-epithelium,  6q 

cone  bipolar  cells,  503 
visual  cells,  503 

rod  bipolar  cells,  503 
visual  cells,  503 
Neurofibrils,  113 

Cajal's  method  of  staining,  34 

importance  of,  in  neurone,  121 
Neuroglia,  73,  94,  125 

mossy  cells  of,  126 

Mailer's  cells  of,  504 

neuroblasts,  iii,  126,  374 

of  cerebellum,  462 

spider  cells,  126 

spongioblasts  of,  126 

technic  for,  127 
Neurokeratin  network,  1:9 
Neurological  staining  methods,  29 
Neuromuscular  bundles,  388 
Neurone,  the,  1 1 1 

axone  of,  116 

caryochromes,  114 

cell  body,  1 1 1 

chromophilic  bodies,  113,  j  14 

contact  theory  of,  122 

continuity  theory  of,  122 

cytoplasm  of,  112 

degenerative  changes  in,  122 

dendrites  of,  1 1  6 

development  of,  i  1  1 

extracellular  network  of,  122 

functional  centre  of,  121 

genetic  centre  of,  121 

Golgi  net,  1  22 

neurofibrils  of,   113,  1  sC> 


Neurone,    Nissl,    special    method    of 
technic  for,  35 
nucleolus,  112 
nucleus,  112 
nutritive  centre  of,  121 
pericellular  network  of,  122 
perifibrillar  substance,  113 
physiological  significance  of,  121 
pigment  in,  115 
retraction  theory  of,  122 
somatochromes,  114 
synapsis  of,  122 
technic  for,  35,  127 
theory,  122 
trophic  centre  of,  121 
Neurones,     afferent    peripheral,     376, 
382 
segmental,  425 
suprasegmental,  278,  426 
associative,  421,  425 
central,  375 
cone  association,  507 
cord,  42  I 

cortical  precentral,  421 
efferent  peripheral,  375,  395,  421 
suprasegmental,  378,  426 
peripheral  segmental,  426 
intermediate,  375,  376 
intersegmental,  426 
peripheral,  376 

afferent,  376,  382,  420,  421 
efferent,  375,  377,  395,  420,  421 
ponto-cerebellar,  452 
rod-association,  507 
somatic  (peripheral),  376 
splanchnic  (peripheral),  376 
suprasegmental  associative,    378 
thalamo-cortical,  414 
visceral  (peripheral),  376 
Neuroplasm,  118 
Neutral  carmine,   18 
Neutrophile  granules,  98 
Nipple,  368 
Nissl  method  for  staining  nerve  cells, 

3  5 
pathological  value  of,   1  1  5 
concerning  chromophilic   l)odies, 

Its 
Nitric  acid  for  decalcifying,  10 

for  dissociating  muscle  tissue,  5 
Nodes  of  Ranvier,  119 
Nodose  ganglion  of  X  nerve,  425 


INDEX. 


569 


Normoblasts,  i68 
Notochord,  anlage  of,  56 
Nuclear  dyes,  1 5 

alum  carmine,  1 7 

basic  anilin,  17 

combination     of     Gage's     and 

Mayer's  formulas,  16 
Delafield's  haematoxylin,  15 
Gage's  haematoxylin,   15 
haematoxylin,  15 
Heidenhain's  haematoxylin,  16 
Mayer's  haemalum,  16 
Weigert's  hasmatoxylin,   17 
eccentricity,  124 
fluid,  44 
groups,  343 
membrane,  43 
sap,  44 

structures,     method    of    demon- 
strating      by       Flemming's 
fluid,  7 
Nuclein,  44 
Nucleolus  of  typical  cell,  44 

false,  44 
Nucleoplasm,  44 
Nucleoreticulum,  44 
Nucleus,  the,  42 

abducentis,  450 
accessory  olivary,  438 
amygdaliformis,  481 
arciform,  477 
arcuatus,  477 
caudatus,  472,  478,  481 
chromatin  of,  44 
Deiterls,  418,  426,  448 
dentate,  41S,  450,  455 
dorsal  cochlear,  441 
Edinger-Westphal,  465 
emboliformis,  450,  455 
facialis,  447 
fastigii,  418,  450,  455 
function  of,  43 
funiculi  cuneati,  414,  426 

gracilis,  414,  426 
globosus,  450,  455 
interstitial,  of  Cajal,  417,  476 
karyoplasm  of,  44 
lenticularis,  477,  478 
linin  of,  44 
membrane  of,  43 
network  of,  44 
nuclein  of,  44 


Nucleus,  nucleoreticulum  of,  44 
nucleolus  of,  44 
oculomotor,  465 

of  acoustic  tubercle,  43  i,  439,  441 
of  a  typical  cell,  42 
of  column  of  Burdach,  414,  430, 

435 
of  Goll,  414,  430,  435 

of  Darkschewitsch,  417 

of  Luys,  469 

of  origin,  377 

oculomotor,  465 

ohvary,  430,  438,  439,  448 

pontis,  464 

pulposus,  180 

red,  417,  41S,  465,  467 

resting,  51 

reticularis  tegmenti,  452 

ruber,  417,  418,  465,  467 

tecti,  418,  450,  455 

terminal,  377 

trapezoid,  441,  449 

triangular,  438 

vestibular,  438,  441,  45° 

von  Bechterew's,  448 
Nuel's  space,  527 
Nutrient  canal,  170 

foramen,  170 

vessels,  of  bone,  170 

Oculomotor  III  nerve,  464,  465 

nucleus,  465 
Odontoblasts,  201,  206,  211 
Oesophagus,  the,  213 
coats  of,  213 
glands  of,  214 
technic  of,  215 
Oil  of  origanum  Cretici   for  clearing 

specimens,  2  i 
Olfactorius  (I  nerve)  ,  477,  492 
Olfactory  bulb,  477,  530 
cells  of,  530 
granule  layer,  530 
layer  of  glomeruli,  530 

of  longitudinal  fibre  bundles, 

531 
of  mitral  cells,  530 
of  olfactory  fibres,  530 
molecular  layer,  530 
olfactory  glomeruli  of,  531 
path,  425,  477,  478,  485 
pallial  commissure,  4 78 


570 


INDEX. 


Olfactory   group   of     segmental   neu- 
rones, 425 
nerve,  425,  477 
organ,  530 

olfactory  bulb  of,  530 

mucosa  of,  264,  530 
technic  of,  532 
tract,  532 
Olivary  nucleus,  430,  437,  439,  448 
Omentum,  235 

gastro-hepatic,  235 
greater,  235 
Opie,  concerning  the  pancreas,  251 
concerning     the     cell-islands     of 
Langerhans,  252 
Oppel's    method    of    staining    intra- 
lobular connective  tissue  of 
liver,  261 
Optic  chiasma,  472,  507 
cup,  516 
decussation,  507 
depressions,  515 
nerve,  425,  467,  47°'  505 
arachnoid  of,  505 
diagram    showing,    with    some 

principal  connections,   509 
dural  sheath  of,  505 
lamina  cribrosa,  506 
pial  sheath,  505 
relation    to    retina   and  brain, 

506 
subarachnoid  space,  505 
subdural  space,  505 
technic  of,  517 
stalk,  5,  15 

tract,  467,  470,  472,  481 
vesicle,  5  i  5 
Opticus  (II  nerve),  425,  467,  470,  492 
Ora  serrata,  498,  501 
Oral  glands,  cells  of,  194 

crescents  of  Gianuzzi,  195 
demilunes  of  Heidenhain,  195 
mixed  glands,  j  94 
mucous  glands,   j  94 
serous  glands,   194 
technic  of,  j  96 
Orange  G,  x8 
Organ  of  Corti,  525 

cells  of  Claudius  of,  527 
Corti's  arches,  526 

tunnel,  526 
IJeiter's  cells,  527 


Organ  of  Corti,  hair  or  auditory  cells, 
526 
Hensen's  cells,  527 
lamina  reticularis  of,  527 
Nuel's  space  of,  527 
phalangeal  processes,  527 
pillar  cells,  525 
of   Giraldes    (paradidymis),    311, 

347 
of  hearing,  518;  see  also  Ear 
blood-vessels  of,  527 
development  of,  529 
ear,  external,  518 

internal,  520 

middle,  519 
lymphatics,  528 
nerves,  528 
technic  of,  529 
of  smell,  530;  see  Olfactory  organ 
olfactory  bulb,  530 

mucosa,  530 

tract,  532 
technic  of,  532 
of  taste,  532 
cells  of,  532 
foliate  papillae,  532 
gustatory  canal,  532 
intergeminal  fibres  of,  533 
intrageminal  fibres  of,  533 
taste  buds,  199,  269,  387,  532 
technic  of,  533 
of  vision,  494 

blood-vessels  of,  511 
development  of,  5 1  5 
eyeball  or  bulbus  oculi,  494 
eyehd,  513 

lacrymal  apparatus,  512 
lens,  510 

lymphatics  of,  512 
nerves  of,  512 
neurone  systems  of,  506 
optic  nerve,  505 
technic  of,  517 
Orgiins,  the,  129 

circulatory  system,  131 
digestive  system,  192 
glands   and    general    structure 
of     muctjus      membranes, 
186 
lymphatic  organs,  J47 
muscular  system,  183 
nervous  system,  373 


INDEX. 


571 


Organs,  reproductive  system,  303 
respiratory  system,  264 
skeletal  system,  164 
skin  and  its  appendages,  351 
special  sense  organs,  494 
urinary  organs,  286 
of    Golgi,    peripheral   nerve  ter- 
minations in,  390 
of  special  sense,  494 
organ  of  hearing,  5  1 8 
of  smell,  530 
of  taste,  532 
of  vision,  494 
Orth's  fluid  (formalin-Miiller's) ,   7 
Osmic  acid  as  a  fixative,  7 
action  on  fat,  7 
on  myelin,  7 
stain  for  fat,  28 
Osseous  labyrinth,  520 
Ossicles  of  middle  ear,  520 
Ossification  centres,  172 
endochondral,  172 
intracartilaginous,  172 
intramembranous,  172 
subperichondral,  172 
subperiosteal,  172 
Osteoblasts,  173 
Osteoclasts,  i  74 
Osteogenetic  tissue,  173 
Otic  ganglion,  390 

vesicle,  529 
Otocyst,  529 

Otolythic  membrane,  522 
Otoliths,  522 

Oval  bundle  of  Flechsig,  418 
Ovary,  the,  323 

blood-vessels  of,  333 
corpora  lutea,  of  pregnancy,  330 
spuria,  332 
vera,  332 
corpus  albicans,  330 
hasinorrhagicum,  329 
luteum,  329 
cortex  of-,  323 
egg  nest,  325 
epoophoron,  ^;^;^ 
Fallopian  tube,  323,  334 
germinal  epithelium  of,  324 
Graafian  follicles,  324 
haematoidin  crystals,  330 
hilum  of,  323 
lutein  cells,  329 


Ovary,  lymphatics  of,  ^^^ 

medulla  of,  323 

nerves  of,  333 

ovarian  stroma,  323 

oviduct,  323,  334 

ovum,  323,  327 

paroophoron,  333 

Pfliiger's  egg  tubes  or  cords,  324 

primitive  ova,  324 

secretion  of,  323 

structure  of,  323 

technic  of,  335 

tunica  albuginea,  324 

zona  vasculosa,  323 
Oviduct,     the,     334;     see     Fallopian 

tubes 
Ovula  Nabothi,  338 
Ovum,  the,  47,  52,  323,  327 

atresia  of  follicle,  t,^^ 

cells  of,  327 

deutoplasm  granules,  328 

development  of,  327,   348,  349 

fertilization  of,  52 

germinal  spot,  327 

maturation  of,  328 

perivitelline  space,  327 

segmentation  of,  56 

yolk  granules  of,  328 

zona  pellucida  of,  327 
Oxyntic  cells,  219 
Oxj'phile  cells,  285 


Pacchionian  bodies,  171,  380 
Pacinian  bodies,  388 

corpuscles,  320,  3S5 
Palate,  mucous  membrane  of,  193 
Palatine  tonsils,  155;  see  Tonsils 
Pallio-pontile  fibres,  464,  479 
Pallial  conections,  413,  414,  416,  421, 

422,  428,  469,  470 
Pallio-spino-peripheral    efferent    con- 
duction path,  41 7 
Pallio-thalamic  fibres,  469,  479 
Pallio-tectal  fibres,  479 
Pallium,  374,  477,  478,  481 

association  cells  of,  483,  484 

cortical  areas  of,  488 

fibres  of,  478,  479,  4S5 
Pancreas,  the,  247 

blood-vessels  of,  252 

cell-islands  of  Langerhans,  250 


572 


INDEX. 


Pancreas,  centro-acinar  cells  of  Lan- 
gerhans,  249 

development  of,  263 

duct  of  Santorini,  247 
of  Wirsung,  247 

epithelium  of  ducts,  248 

excretory  ducts,  247,  248 

intracellular  secretory  tubules  of, 
250 

lobules  of,  247 

lymphatics  of,  252 

nerves  of,  252 

Opie,  concerning  cell-islands,  252 

secondarj^     excretory     dvict     of, 
247 

secretion  of,  249 

sustentacular  cells  of,  250 

technic  of,  252 

terminal  tubules  of,  248 

zymogen  granules  of,  248 
Paneth,  cells  of,  228 
Panniculus  adiposus,  353 
Papillae,  circumvallate,  198 

compound,  352 

filiform,  197 

fungiform,  198 

nerve,  352 

simple,  352 

vascular,  352 
Paradidymis,    or    organ    of    Giraldes, 

311.  347 
Paraffin  embedding,  12 
apparatus  for,  13 

oven,  12 

section-cutting,  14 

sections,  staining  and  mounting 
of,  21 
Paramiton,  41 
Paranuclein,  44 
Paraplasm,  42 
Parathyreoids,  283 

chief  or  clear  cells  of,  285 

development  of,  285 

function  of,  285 

oxyphile  cells,  285 

Pool's  theory  of,  285 

structure  of,  283,  284 

technic  of,  285 
Pareleidin,  355 

Parenchyma  of  glands,  188,  243 
parietal  cells,  219 
Paroojjhoron,  333 


Parotid  gland,  243 

development  of,  263 

intercalated  tubule  of,  244 

nerves  of,  241 

Stenoni's  duct  of,  243 

technic  of,  247 
Parovarium,  313 
Pars  ciliaris  retinas,  499,  501,  505 

iridica  retinae,  501,  505 

optica  retinae,  501 

papillaris,  352 

reticularis,  351 
Peduncle,  inferior,  447,  449 

middle,  447 

superior,  447,  450,  452,  454,  464, 

47o>  477 
Peduncles,  cerebral,  464 
Pellicula,  42 
Penicillus,  161 
Penis,  319 

arteries  of,  320 

cavernous  sinuses,  320 

corpora  cavernosa  of,  319 

corpus  spongiosum  of,  319 

erectile  tissue,  319 

glans,  321 

glands  of  Tyson  of,  321 

lymphatics,  320 

nerve  endings  of,  320 

prepuce  of,  321 

sebaceous  glands  of,  321 

technic  of,  322 

tunica  albuginea  of,  319 
Peptic  glands,  219 
Perforated  space,  anterior,  477,  481 
Perforating  fibres,  168 

of  cornea,  496 

of  Sharpey,  168 
Perforatorium,  314 
Periaxial  sheath,  118 
Pericardial  cavity,  144 
Perichondrium  of  bone,  175 

of  cartilage,  92 
Perichorioidal  lymph  spaces,  497 
Pericranium,   173 
Peridental  membrane,  205 
Peri  fascicular  sheath,  184,  382 
Perifibrillar  substance,  113 
Perilymph,  520 
Perimysium,  184 
Perineurium,  382 
Periosteal  buds,  176 


INDEX. 


573 


Periosteum,  167,  174 
dental,  205 
primary,  175 
Peripheral  afferent  neurones,  376,  382 

cerebro-spinal  ganglia,  3S2 

sj^mpathetic  ganglia,  390 
efferent  neurones,  377,  395 
motor  neurone  system,  395 
nerves,  376 

aft'erent  part  of,  380 

cranial,  380 

efferent  part  of,  380 

endoneurium  of,  382 

epineurium  of,  381 

fascicles  of,  381 

intrafascicular  connective  tis- 
sue of,  382 

medullated  fibres  of,   117,   118 

motor  or  eft'erent,  380 

motor  nerve  terminations,  395 

non-medullated  fibres  of,   117, 
118 

perifascicular  sheath  of,  382 

perineurium  of,  382 

sensory  or  afferent,  380 

sensory  nerve  terminations,  385 

sheath  of  Henle,  382 

spinal,  380 

structure  of,  380 

technic  of,  382 
nerve  terminations,  386 

annular,  387 

end-bulbs,  386,  388 

free  endings,  386,  394 
in  penis,  320 

in  mucous  membrane  of  mouth 
and  conjunctiva,  387 

in     muscle-tendon     junctions, 

387 

in  skin,  365,  386 

in  smooth  muscle,  388,  394 

in  voluntary  muscle,  388 

Krause's  end-bulbs    in    penis, 
321 

Meissner's    corpuscles  in   pap- 
illae of  penis,  321 

muscle  spindles,  388 

muscle-tendon  organs  of  Golgi, 
390 

neuromuscular  bundles,  388 

Pacinian  bodies,  388 

corpuscles    of    penis,  320 


Peripheral   nerve   terminations,   Ruf- 
fini's  theory  of,  388 
spinal  nerves,  380 
spiral  terminations,  388 
tactile  cells,  386 
corpuscles,  386 
meniscus,  386 
taste  buds,  387,  533 
Peritoneal  cavity,  144 
Peritoneum,  235 
parietal,  235 
subserous  tissue  of,  235 
visceral,  235 
Perivitelline  space,  327 
Permanent  teeth,  208,  211 
Perpendicular  pontile  fibres,  453 
Pes  pedunculi,  374,  427,  464,465,470 
Petit,  canal  of,  511 
Petrosal  ganglion  of  IX,  425 
Peyer's  patches,  228 
Pfliiger's  egg  tubes  or  cords,  324,  349 
Phseochrome  granules,  299 
Phaeochromoblasts,  302 
Phagocytes,  98,  152 
Phagocytosis,  98 
Phalangeal  processes,  527 
Pharyngeal  tonsils,   157;  see  Tonsils 
Pharynx,  the,  212 

blood-vessels  of,  213 
lymphatics  of,  213 
nerves  of,  213 
structure  of,  212 
technic  of,  213 
Pia  mater,  380 

blood-vessels  of,  3 So 
cerebralis,  380 

Pacchionian  bodies,  380 
spinalis,  380 
technic  of,  iSo 
Picric  acid  as  a  fixative,  8 

as  plasma  dye,  18 
Picro-acid-fuchsin,  18 
Picro-carmine,  19 
Pigment  granules  in  cells,  42,  355 
in  connective  tissue,  77 
in  epithelium,  64 
in  nerve  cells,  116 
Pillar  cells,  525 
Pineal  body,  490 

brain  sand  of,  490 
technic  of,  290 
Pineal  eye,  490 


574 


INDEX. 


Pinna,  51S 
Pituitary  body,  489 

anterior  lobe  of,  489 

Berkley,      concerning      posterior 
lobe,  490 

posterior  lobe  of,  490 

technic  of,  490 
Placenta,  341 

blood-vessels  of,  344 

canalized  fibrin,  343 

cell  patches,  343 

chorionic  villi,  341 

cotyledons,  341 

fastening  villi,  341 

foetalis,  341 

free  or  floating  villi  of,  341 

lymphatics  of,  345 

membrana  chorii  of,  341 

nerves  of,  345 

nuclear  groups,  343 

septa  of,  344 

subchorionic    placental    decidua, 

344 

syncytium  of,  343 

technic  of,  349 

uterina,  343 

villi  of,  341 
Plasma  cells,  75 
Plasma  dyes,  i  7 

acid  aniline,  18 

eosin,  i  7 

neutral  carmine,  18 

picric  acid,  18 
Plasmosome,  44 
Plastids,  41 
Plastin,  40 
Pleura,  parietal,  273 

pulmonary,  273 
Pleural  cavity,  144 
Pleuroperitoneal  cleft,  144 
Plexiform  layer  of  Cajal,  482 
Plexus  annularis,  5  i  2 

Auerbach's,  225,  230,  232,  238,390 

ciliary,  5  i  2 

chorioideus,  431,  450 

Heller's,  236 

Meissner's,  222,  238,  390 

myentericus,  238 

prevertebral,  390 
Plicae  palmataj,  338 

Pneumogastricus  (vagus  nerve),  425, 
43  7.  403 


Polar  bodies,  ^^ 

rays,  48 
Polymorphonuclear  leucocytes,  97 
Polymorphous  cells,  482 
Polynuclear  leucocytes,  97,  152 
Pons  Varolii,  427,  374,  431,  447,  449 
longitudinal  fibres  of,  449 
perpendicular  fibres,  449,  453 
pontile  nuclei  of,  449 
pyramid  of,   449 
transverse  fibres  of,  449 
Pool,  E.  H.,  concerning  parathyreoid 

gland,  285 
Portal  canal,  255 

vein,  254 
Posterior  columns  of  spinal  cord,  397, 
401 
origin  of  fibres  of,  396,  397 
column  of  Burdach,  408 

of  GoU,  408 
commissure,  468,  472 
distribution  of  fibres  of,  414 
horns,  398,  401 
longitudinal  fasciculus,  439 
median  septum,  401 
nerve  root,  403 

root  fibres,  403 
nucleus  funiculi  cuneati,  414 
funiculi  gracilis,  408 
of  the  column  of  Burdach,  414 
of  the  column  of  GoU,  414 
tract,    or   terminal   zone   of   Lis- 

sauer,  397,  403 
zone  of  Lissauer,  397 
Potassium  hydrate,   as  a  macerating 

fluid,  4 
Precapillary  artery,  134 
Predorsal  fasciculus,  452,  464 
Prepuce,  321 

Preparation  of  sections,  5 
Preserving,  9 

Prevertebral  plexuses,  390 
Primary  germ  layers,  5O 

renal  vesicles,  348 
Primitive  ova,  324 
Projection  fibres,  469,  47°.  47^.  479 
Pronephric  or  Wolffian  ducts,  347 
Prone]jhroi,  346 
Prcjnucleus,  female,  53 

male,  53 
Prophase,  48 
Proprio-ceptors,  390 


INDEX. 


oto 


Prosencephalon,  373 
Prostate  gland,  317 

blood-vessels  of,  318 

capsule  of,  317 

corpora  amylacea  of,  317 

crescentic  corpuscles  of,  317 

epithelium  of,  317 

lymphatics  of,  318 

Miillerian  duct,  318 

nerves  of,  318 

technic  of,  319 

trabeculae,  317 

urethra,  317 

uterus  masculinus,  318 

utriculus  prostaticus,  317,  318 

vesicula  prostatica,  317 
Protargol,    for    staining    intercellular 

substance,  26 
Protoplasm,  39,  41 

streaming  of,  47 

theories  of  structure  of,  40 
Protoplasmic  movement,  47 

processes,  1 1 1,  116 
Proximal  convoluted  tubule,  290,  292 
Prussian  blue  gelatin  as  an  injecting 

fluid,  23 
Pseudopodia,  46 
Pulvinar  radiations,  470 

thalami,  470,  472 
Pulmonary  artery,  278 

lobule,  273,  278 

pleura,  273 
Pulp  cavit}^  200 

cords,  161 

of  Mall,  162 

splenic,  161 
Purkinje  cells,  456,  461 
Putamen,  481 
Pyloric  glands,  219 
Pylorus,  230 
Pyramid,  cortical,  281 

of  Ferrein,  288 

Malpighian,  288 
Pyramidal  cells,  482 

decussation,  416,  429 
tracts,  416,  479 

anterior    pyramids,    416,    431, 

447.  454 
crossed  pyramidal,  416 
direct  pyramidal,  417 
pyramidal  decussation,  4  i  6 
of  Tiirck,  direct  pyramidal,  417 


Pyramids,  3  74 
Pyrenin,  44 
Pyriform  lobe,  477 

Racemose  glands,  188 

Radiations  of  Meynert,  485 

Radix  spinalis,  V,  425 

Rami  communicantes,  gray,  351,  392 

white,  381,  390,  391,  395 
Ranvier's    alcohol    as    a    macerating 
fluid,  4 
nodes  or  constrictions  of,  iig 
showing  muscle  fibres,   103 
Raphe,  of  semicircular  canals,  522 

median,  436,  438 
Receptors,  376,  390,  424,  425 
Receptor  to  effector,  direct  path,  423 
Rectum,  234 
anus,  234 

columnse  rectales,  234 
technic  of,  241 
Red  blood  cells,  95;  see  also  Blood 
nucleated,  161,  168 
bone  marrow,  168 
nucleus,  417,  418,  465,  467 
Reduction  of  chromosomes,  315 
Reflex  arc,  cerebellar,  421 
cerebral,  421 
disynaptic,  42  i 
monosynaptic,  420 
pallial,  42  I 

three-neurone  spinal,  421 
two-neurone  spinal,  420 
Reissner,  membrane  of,  524 
Remak,  fibres  of,  117 
Renal  corpuscle,  288 

development  of,  288,  347 
Renculus,  286 
Replacing  cells,  65,  220 
Reproduction  of  cells,  47 
Reproductive  system,  303 

development  of,  314,  324,  346 
rudimentary     structures     con- 
nected with  the,  311 
female  organs,  323 
clitoris,  346 
Fallopian  tube,  334 
ovary,  323 
oviduct,  334 
placenta,  341 
urethra,  32  i 
uterus,   ;  ;6 


576 


INDEX. 


Reproductive  system,  female  organs, 
vagina,  345 
vestibule,  346 
male  organs,  303 

Cowper's  glands,  319 
ejaculatory  ducts,  311 
penis,  319 
prostate  gland,  317 
seminal  ducts,  309 

vesicle,  311 
seminiferous  tubule,  304 
spermatozoa,  313 
testis,  303 
urethra,  321 
Respiratory  bronchus,  274 
cells,  274 
epithelium,  295 
Respiratory  system,  264 
bronchi,  269,  274 
development  of,  279 
general  references    for    further 

study,  285 
larynx,  266 
lungs,  273 
nares,  264 

technic  of,  269,   280,  285 
trachea,  266 
Restiform  body,  430,  438,  439 
Rete  testis,  tubules  of,  304,  309 

vasa  efferentia,  309 
Reticular  formation,  419,426,  431,433, 

437.  439.  447.  449.  452,  454 

glands,  190 

process,  401 

tissue,  83 
Retina,  501 

blood-vessels  of,  511 

cells  of,  501,  502,  503,  504 

ellipsoid  of  Krause,  503 
fibre-baskets  of,  505 

fovea  centralis,  505 

ganglionic  layer  of,  501 

horizontal  cells  of,  503 

inner  limiting  membrane  of,  504 
molecular  layer,  504 
nuclear  layer,  503 

layer  of  nerve  cells,  504 
of  nerve  fibres,  504 
of  neuro-epithelium,  502 
of  pigmented  eijithelium,  501 
of  rods  and  cones,  502 

macula  lutea,  505 


Retina,  Miiller's  cells  and  fibres,  504 
ora  serrata,  501 
outer  limiting  membrane,  504 
molecular  layer,  503 
nuclear  layer,  502 
pars  ciliaris  retinse,  501,  505 
iridica  retina,  501,  505 
optica  retinae,  501 
relation  to  optic  nerve,  506 
rod  and  cone  cells  of,  503 
visual  purple  of,  503 
Retinaculse  cutis,  353 
Retrolenticular    portion    of    internal 

capsule  (Cirl),  472 
Retzius,  lines  of,  204 
Rhinencephalon,  477,  478 
Rhinopallium,  477 
Rhombencephalon,  373,  429 
Ribboning  paraffin  sections,  14 
Rod  association  neurones,  507 

fibres,  503 
Rod-visual  cells,  502 
Rods,  layer  of  rods  and  cones,  502 
Rolando,  gelatinous  substance  of,  437 
RoUett's   theory   of   striated   muscle, 

104 
Root  canal,  200 

cells,  398 
Roots,  afferent,  376 
Ruffini,  corpuscles  of,  365 

theory  of  nerve  terminations,  388 
Rugae,  216,  218,  345 
Riihle,     cohcerning     the     uriniferous 
tubule,  293 

Saccular  glands,  187,  190 
Saccule,  521 

and  utricle,  521 

auditory  hairs  of,  522 

macula  acustica,  521 

neuro-epithelial  cells  of,  521 

otolithic  membrane  of,  522 

otoliths  of,  522 

sustentacular  cells  of,  521 
Sachs,  E.,  concerning  thalamus,  469, 

470 
Sacral  segments  of  spinal  cord,  396 
Safranin,  17 

Salivary  corpuscles,   157 
glands,  193,  242 

blood-vessels  of,  245 

capsule  of,  242 


IXDEX. 


577 


Salivary      glands,     development     of, 
263 
ducts  of,  242 
interstitial  tissue,  243 
lobes  of,  242 
lobules  of,  242 
lymphatics  of,  245 
minute  structure  of,  194 
nerves  of,  246 
parenchyma  of,  243 
parotid,  the,  243 
secretory  tubules  of,  242 
sublingual,  the,  243 
submaxillary,  the,  244 
trabeculse  of,  242 
technic  of,  247 
tubules  of,  242 
Santorini,  cartilage  of,  266 

duct  of,  247,  266 
Sarcolemma,  102 
Sarcoplasm,  102 
Sarcostyles,  185 

Sarcous  elements  of  Bowman,  103 
Satellite  cells,  383 
Scala  media,  523 
tympani,  523 
vestibuli,  523 
Scarpa's  ganglion,  425 
Schafer    and    Opie    concerning    cell- 
islands  of  Langerhans,  252 
Schlemm,  canal  of,  500 
Schmidt-Lantermann,  clefts  of,  11 
incisions  of,  iig 
segments  of,  119 
Schreger,  incremental  lines  of,  202 
Schultze,  comma  tract  of,  419 
Schwalbe,  lymph  paths  of,  512 
Schwann,  sheath  of,  116,  119 
Sclera,  the,  494 

lamina  cribrosa  of,  494 
fusca  of,  494 
Scrotum,  skin  of,  303 
Sebaceous  glands,  264,  355,  362 
development   of,    366 
of  glans  penis,  355 
of  labia  minora,  355 
of  margin  of  lips,  264,  355 
of  prepuce,  355 
Sebum,  363 

Secondary  cochlear  tract,  441 
trigeminal  tract,  433 
vestibular  tract,  441 


Secretion,  239 
Secretory  tubules,  242 

Golgi  method  of  demonstrating,  26 

of  parietal  cells  of  stomach,  219 
Section  cutting,  13 

celloidin  specimens,  14 

paraffin  specimens,  14 

staining,  15 
Segmental  brain,  377,  425 

nerves,  377,  425 
Segmentation  cavity,  55 

of  ovum,  56 
Segments     of     Schmidt-Lantermann, 
119  • 

of  spinal  cord,  396,  409,  410,  411 
Semen,  313 

Semicircular  canals,  520,  522 
crista  acustica  of,  522 
cupula  of,  522 
raphe  of,  522 
semilunar  fold  of,  522 
Seminal  ducts,  309 

epididymis,  309 
vas  deferens,  310 
vasa  efferentia,  309 

vesicles,  311  '  ■ 

Seminiferous  tubules,  304 

cells  of,  304 

columns  of  Sertoli,  305 

convoluted  portion  of,  304 

development  of,  349 

glandular  cells  of,  305 

rete  testis,  304,  309 

spermatids,  307 

spermatocytes,  307 

spermatogenic  cells,  305 

spermatogones,  306 

spermatozoa,  307 

straight  portion  of,  304 

supporting  cells  of,  305 

sustentacular  cells  of,  305 
Semilunar  ganglion  of  V,  425 
Senses,  common,  390,  425 

general,  390 

special,  390 
Sensory  decussation,  435 

path,  general,  390,  413,  414,  425, 
452,  470,  485 

peripheral  nerves,  3 So 
Septa  renis,  2 88;  see  Kidney 
Septo-marginal  tract,  418 
Septum  linguae,  197 


578 


INDEX. 


Serial  sections,  14 
Serous  membranes,  144 
Sertoli,  cells  of,  305,  315 

columns  of,  305 
Sex  cells,  348,  349 
Sharpey,  showing  bone  lamellae,  167 
Sharpey's  fibres,  168,  205 
Sheath  of  Henle,  120,  382 

medullary,  117,  119 

of  Schwann,  117,  119 

perifascicular,  382 
Sherrington  concerning  receptors,  390 
Signet-ring  cell,  86 
Silver-nitrate  method  of  staining  inter- 

•     cellular  substance,  26 
Skein,  closed,  49 
Skeletal  system,  164 

articulations,  180 

bone-marrow,  168 

bones,  164 

cartilages,  180 

general    references     for     further 
study,  182 

technic  of,  171,  179,  181 
Skin  and  its  appendages,  351 

blood-vessels  of,  364 

color  of,  355 

corium,  351 

corpuscles  of  Grandry,  386 
of  Meissner,  365,  387 
of  Ruffini,  365 
of  Wagner,  365 

cuticle,  353 

derma,  351 

development  of,  366 

eleidin  of,  354 

end-bulbs  in,  386 

epidermis  of,  353 

glands  of,  355 

glandulae  sudoriparse,  355 

Golgi-Mazzoni  corpuscles  of,  365 

hair  follicles  of,  359 

junction  of,   with  mucous  mem- 
brane of  mouth,  193,  264 

keratohyalin  granules,  354 

Krause's  end-bulbs,  365 

lymphatics  of,  365 

mammary  gland,  368 

Merkel's  corpuscles  of,  386 

mitosis  of  cells  of,  354 

nails,  356 

nerves  of,  365,  386 


Skin,  of  scrotum,  352 

Pacinian  bodies  of,  38S 

panniculus  adiposus  of,  353 

papilla;  of,  352 

pareleidin,  355 

pars  papillaris,  352 

pars  reticularis,  351 

peripheral  nerve  terminations  in, 
386 

prickle  cells  of,  354 

retinaculse  cutis,  353 

sebaceous  glands  of,  355 

subcutaneous  tissue  of,  352 

sweat  glands   (glandulse  sudorip- 
arse), 355 
pores  of,  355 

tactile  cells  of,  386 
corpuscles,  365,  387 

technic  of,  355 

for  blood-vessels  of,  366 

Vater-Pacinian  corpuscles  of ,  365 
Small  intestines,  223 

agminated  follicles,  228 

Auerbach's  plexus,  230,  238 

blood-vessels  of,  326 

Brunner's  glands  of,  230,  239 

cells  of,  226,  227 

chyle  capillaries  of,  237 

coats  of,  224 

crypts  of  Lieberkiihn,   224,   228, 
230.  239 

development  of,  262 

lacteals  of,  227,  236,  237,  240 

lymphatics,  237 

Meissner's  plexus,  230,  238 

muscle  of,  230 

nerves  of,  238 

Peyer's  patches  of,  228 

plexus  myentericus,  238 

replacing  cells,  227 

secreting  cells,  225 

solitary  follicles,  228 

technic  of,  241 

valvulae  conniventes  of,  216,   223 

villi  of,  224,  237 
Smooth  muscle,    joi;  see  Involuntary 

^nuscle 
vSoflium     hydrate     as     a     macerating 

(iuid,  4 
Solitary  fasciculus,  438,  439 

follicles,  221,  228 
Somatic  fperi]jheral)  neurones,  376 


INDEX. 


579 


Somatochromes,  114 
Spaces  of  Fontana,  500 
Spalteholz,  iq6 
Spermatids,  307,  314 
Spermatoblast,  316 
Spermatocytes,  307,  314 
Spermatogenesis,  313 

technic  of,  317 
Spermatogones,  306,  314,  349 
Spermatozoa,  52,  307,  313 
acrosome,  314 
apical  bod}^  314 
development  of,  52,  314 
diagram  of,  53,  313 
galea  capitis,  313 
perforatorium,  314 
structure  of,  ^2,  314 
technic  of,  317 
Sphenopalatine  ganglion,  390 
Spider  cells,  i  26 
Spinal  accessory  nerve,  493 
Spinal  cord,  396 

anterior  columns  of,  401 
horns  of,  398,  401 
marginal  bundle  of  Lowenthal, 

41S 
median  fissure,  401 
nerve  roots  of,  403,  412 
p^j^ramids,  416 
white  commissure  of,  403 
antero-lateral  columns  of,  401 
ascending  tract,  4 1 5 ;    see  Ven- 
tral s  pino-cerebellar 
descending  tract,  418 
arachnoid  membrane  of,  380 
arrangement  of  fibres  of,  405 
arteries  of,  406 
ascending  tracts  of,  413,  426 
blood-vessels  of,  406 
cell-groupings  of,  403 
cells  of  dorsal  horn,  403 
cells    of    the    intermediate    gray 
matter,  403 
of  Golgi,  Type  II,  3()g 
of  ventral  horn,  404 
central  canal  of,  373 

gelatinous  substance,  402 
cervical  enlargement  of,  396 

segments  of,  396 
Clarke's  colunin  of,  403,  40S 
coccygeal  seginents  of,  ^,q(^ 
column  of  Burdach,  40S,  414 


Spinal  cord,  column  of  Goll,  408,  414 
cells,  398 

hecateromeric,  398 
heteromeric,  398 
tautomeric,  398 
comma  tract  of  Schultze,  419 
conduction  paths  of,  377,  417 
cornua  of,  401 

crossed  pyramidal  tract,  416 
descending    paths    from    higher 
centres,  419,  427 
tract     from    Deiter's    nucleus, 
418 
from  vestibular  nuclei,  418 
diagram  showing  tracts  of,  412 
direct  ascending  paths  to  higher 
centers,  413,  415.  423 
cerebellar  tract,  415 
pyramidal  tract,  417 
reflex  collaterals,  405 
dorsal  gray  columns,  401 
commissure,  402 
spino-cerebellar  tract,  415 
white  columns,  401 
dura  mater  of,  370 
ependyma  of,  406 
fasciculus,    medial    longitudinal, 
418 
of  Thomas,  418 
fibre  tracts  of,  408 

methods  of  determining,  40S 
filum  terminale  of,  396 
finer  tructure  of,  405 
fundamental    columns    of,     399, 

419 
ganglion  cells  of,  397 
gelatinous  substance  of  Rolando, 

402 
general  topography  of,  401 
Gowers'  tract,  416 
gray  matter  of,  377,  401 
ground  bundles  of,  399.  41Q 
H  el  wag's  tract,  418 
interchange  of  fibres,  405 
intermediate  gray  matter,  403 
intermedio-lateral  column,  403 
lateral  horn  of,  403 
long    ascending    arms    of    dorsal 

root  fibres,  413 
longitudinal  section  of  six  days' 

chick  embryo,  401 
lumbar  enlargement  of,  396 


580 


INDEX. 


Spinal  cord,  lumbar  segments  of,  396 
main  motor  fibre  systems  of,  395, 

420 
marginal    bundle    of    Lowenthal, 

41S 
marginal  zone,  402 
medullated  fibres  of,  395,  406 
membranes  of,  378 

arachnoid,  380 

blood-vessels  of,  380 

dura  mater,  379 

pia  mater,  380 

technic  of,  380 
mixed  spinal  nerve,  425,  452,  492 
motor  cells  of  anterior  horn,  398 
multipolar  ganglion  cells  of,  112, 

384,  397 
neuroglia  cells,  406 

fibres,  406 

tissue,  403 
neurone  systems  of  371,  420,  421 
nucleus,  Darkschewitsch's,  417 

Deiter's,  418 

funiculi  cuneati,  414 
gracilis,  414 
origin  of  fibres  of  white  matter, 
396 

of   posterior   columns  of,  397 
oval  bundle  of  Flechsig,  418 
peripheral     motor     or     efferent 
neurone  system,  375    395 

sensory    or    afferent    neurone 
system,  376,  382 
pia  mater,  379,  401 
plexus  of  fine  fibres,  405 
posterior  columns,  397 

funiculus,  401,  413 

horns,  398,  401 

median  septum,  401 

nerve  roots,  403 

root  fibres,  403 
postero-lateral  grooves,  401 

sulci,  40  r 
pyramidal  decussation,  416 

tracts,  416,  426 
reflex  arcs,  420 
reticular  process,  401,  408 
root  cells,  398 
rubro-spinal  tract,  417 
sacral  segments  of,  396 
scheme  of  neurone  relations  of, 
412 


Spinal  cord,  section  through  cervical 
enlargement  of,  408 
through   lumbar   enlargement, 

401 
through    mid-thoracic    region, 

408 
through  six-day  chick  embryo, 

400 
through  twelfth  thoracic   seg- 
ment, 408 
segments  of,  396,  409,  410,  411 
septo-marginal  tract,  418 
shape  of,  396 

short  fibre  systems  of,  399,  419 
size  of,  396 

spino-tectal  tract,  415 
-thalamic  tract,  414 
tecto-spinal  tract,  417 
technic  of,  421 
thoracic  segments  of,  396 
tract  from  interstitial  nucleus  of 

Cajal,  417 
tractus  cerebro-spinalis,  416 
cortico-spinalis,  416 
pallio-spinalis,  ,416 
reticulo-spinalis,  419 
spino-cerebellaris  dorsalis,  415 
spino-spinalis,  419 
ventralis,  415 
variations    in    structure    at    dif- 
ferent levels,  407 
veins  of,  407 

ventral  gray  columns,  401 
commissure,  402 
white  columns,  401 
vestibulo-spinal  tract,  418 
von  Monakow's  tract,  417 
white  commissure,  403 

matter,  377,  396 
zona  spongiosa,  402 

terminalis,  403 
zone  of  Lissauer,  403 
Spinal  ganglia,  382 

amphicytes,  383 
capsules  of,  383 
development  of,  375 
technic  of,  394 
ganghon  cells,  390,  397 
ascending    arms    from    central 

processes  of,  390 
central  processes  of,  390 
classification  of,  383 


INDEX. 


581 


Spinal  ganglion  cells,  collaterals  from, 

384 
descending  arms  from  central 

processes  of,  390 
development  of,  375 
Dogiel's  classification,  383 
ectodermic  origin,  373 
modes  of  termination  of    per- 
ipheral processes  of,  385 
peripheral  processes  of,  3S5 
relation  to  dorsal  roots,  376 
Ruffini's  classification  of  termi- 
nations in  muscle  spindles, 
388 
satellite  cells,  383 
structure  of,  382 
technic  of,  394,  399 
Spinal  nerves,  380 
Spindle,  achromatic,  48 
Spino-cerebellar  tract  (dorsal)  415,426 

(ventral),  415,  426 
Spino-peripheral   motor  neurone  sys- 
tem, 375,  395 
Spino-tectal  tract,  415,  433,  437,  439, 

447,  450 
Spino-thalamic  tract,  414,    431,  450, 

452,  453-  465 
Spiral  ganglion,  425,  528 

ligament,  523 

organ,  525 

prominence,  525 

terminations,  388 
Spireme,  closed,  49 

open,  49 
Spireme-thread,  50 
Splanchnic  (peripheral)  neurones,  376 
Spleen,  15S 

ampulte,  161 

blood-vessels,  160 

cavernous  veins,  161 

cells  of,  161 

central  arteries  of,  160 

connective  tissue  framework,  159 

cords  of,  161 

corpuscles  of,  160 

ellipsoids  of,  160 

germinal  centres  of,  159 

lymphatics  of,  162 

Mall's  theory  of  vascular  chan- 
nels of  pulp,  162 

Malpighian  bodies,  i^q, 

nerves  of,  162 


Spleen,  penicillus,  161 
pulp  of,  159,  161 

cords  of,  161 
spindles  of,  160 
technic  of,  163 
Splenic  corpuscles,  159 

pulp,  159,  161 
Spheno-lymph  nodes,  152 
Spongioblasts,  115 

of  His,  374 
Spongioplasm,  40 
Spongy  bone  (cancellous)  164,  174 

primary,  177 
Staining,  1 5 

differential,  3 

double  with  haematoxylin-eosin, 

18 
in  bulk,  19 
methods,  special,  26 

Golgi's  chrome  silver  for  secre- 
tory tubules,  26 
Jenner's,  for  blood,  28 
Mallory's  aniline  blue  for  con- 
nective tissue,  28 
phosphomolybdic  acid  haem- 
atoxylin     stain    for     con- 
nective tissue,  27 
phosphotungstic  acid  hsema- 
toxylin  stain   for  connec- 
tive tissue,  27 
osmic  acid,  for  fat,  28 
silver  nitrate,  for   intercellular 

substance,  26 
Weigert's     elastic-tissue  stain, 
26 
paraffin  sections,  20 
sections,  18 

double    with    htematoxylin- 

eosin,  18 
triple      with     hasmatoxylin- 

picro-acid-fuchsin,  19 
with  picro-acid-fuchsin,  18 
with  picro-carmine,  19 
selective,  3 

special  neurological  methods,  29 
Cajal's     methods     for     neuro- 
fibrils in  nerve  cells,  34 
Golgi  bichlorid  method,  ^t, 

silver  method,  32 
Marchi's,  for   degenerating 

nerves,  3  i 
Nissl's  method,  35 


582 


INDEX. 


Staining,    Weigert's,    for    niediiUated 
nerve  fibres,  2g 
Weigert-Pal  method,  30 
Stains,  nuclear  dj^es,  15 

plasma  d^^es,  i  7 
Stalked  hydatid,  312 
Stapes,  520 
Stellate  cells,  457,  482 
Stenoni,  duct  of,  243 
Stomach,  217 

acid  cells  of,  21Q,  23Q 

adelomorphous  cells  of,  219 

Auerbach's  plexus,  225 

blood-vessels  of,  326 

chief  cells  of,  219,  239 

delomorphous  cells  of,  219 

development  of,  262 

epithelium  of,  218 

fundus  glands  of,  219 

gastric  crypts  of,  218 
glands  of,  218 
pits  of,  218 

lymphatics  of,  237 

mucous  membrane  of,  218 

muscular  coat  of,  221 

nerves  of,  238 

parietal  cells  of,  219,  239 

peptic  cells  of,  219,  239 
glands  of,  2  1 9 

pyloric  glands  of,  219,  220 

rugae  of,  216,  218 

secretion  of,  239 

solitary  follicles  of,  2  2  l 

stroma  of,  220 

technic  of,  223 
Stohr,  scheme  of  spleen,  160 
Stomata,  145 
Stratum  cinereum,  468 

corneum,  354 

cylindricum,  353 

fibrosum,  181 

germinativum,  354 

granulosum,  354 

lemnisci,  468 

lucidum,  354 

Mal]jighii,  353 

mucosum,  353 

opticum,  468 

spinosum,  354 

zonale,  467 

synoviale,  j8i 
Streaming  of  protoplasm,  47 


Stria  meduUaris,  477,  4 78 

terminalis,  477 

vascularis,  525 
Strise  thalami,  468 
Stroma  of  mucous  membranes,  191 

of  the  red  blood  cell,  96 
Styloglossal  fibres,  197 
Subchorionic  placental  decidua,  344 
Sublingual  gland,  243 

crescents  of  Gianuzzi  of,  244 

development  of,  262 

duct  of  Bartholin  of,  244 

nerves  of,  246 

technic  of,  247 
Sublingualis  minor,  244 
Submaxillary  ganglion,  390 

gland,  244 

development  of,  262 
duct  of  Wharton  of,  244 
nerves  of,  246 
technic  of,  247 
Submucosa,  191 
Subperichondrial      ossification,      172, 

177 
Subperiosteal  ossification,   172,   177 
vSubstantia  alba,  377 

grisea,  377 

nigra,  464,  465,  467,  470 

pro]jria  corneae,  496 
Sulcus,  external  spiral,  525 
Superior    cerebellar    peduncles,     447, 

45°.  452,  454,  464 

coUiculus,  467 

ganglion  of  IX,  425 

longitudinal  fasciculus,  479,  481 

olive,  451 
Suprarenal  gland,  299 

blood-vessels  of,  300 

chromaffin  granules,  299 

development  of,  301 

lipoid  granules,  299 

lymphatics,  301 

nerves  of,  30 j 

phaeochrome  granules,  299 

])haeochromoblasts,  302 

sympiithoblasts,  302 

technic  of,  302 
Supraradiary  i)lcxus,  4S5 
Su])r£isegmenla1  brain,  424,  427 
cerebral  heniis])heres,  427 
connections    (afferent    and    ef- 
ferent), 426,  42  7 


IXDEX. 


5S3 


Suprasegmental  brain,  corpora  quad- 
rigemina,  42  7 
intersegmental  nuclei  and  tracts 

of  segmental  brain,  427 
nuclei  and  tracts  forming  supra- 
segmental paths,  427 
pallium,  427 

peripheral     (segmental)      neu- 
rones, 427 
terminal  nuclei,  427 
neurones,  378 
afferent,  378 
associative,  378 
efferent,  378 
Suspensory  ligament,  510 
Sustentacular    cells,     250,     265,   305, 

521 
Sweat  glands,  355 

development  of,  366 
ducts  of,  355 
muscle  tissue  of,  368 
pore,  3S5 
Sympathetic  ganglia,  390 
cells  of,  392 
chain  ganglia,  390 
development  of,  375 
in  Auerbach's  plexus,  390 
in  Meissner's  plexus,  390 
pigmentation  of  cells  of,  392 
prevertebral  plexuses,  390 
structure  of,  390 
technic  of,  394 
termination  of  nerves,  394 
vertebral  ganglia,  390 
nervous  system,  373 
Synapsis  of  neurones,  122 
Synarthrosis,  180 
Synchondrosis,  180 
Syncytial  cells,  374 
Syncytium,  62,  108,  343 
Syndesmosis,  180 
Synovial  membrane,  t8i 

viUi,  181,  182 
Szymonowicz,     showing    intercellular 
bridges,  66 
showing  medullated  nerve  fibre, 
119 

Tactile  cells,  386 

corpuscles,  196,  386 

of  Meissner,  387 

of  Wagner,  387 
meniscus,  386 


Taenia  thalami,  477 
Tapetum  cellulosum,  497 

fibrosum,  497 
Tarsal  glands,  514 
Tarsus,  514 

Taste  buds,  199,  269,  387,  533 
Tautomeres,  398,  404 
Teasing,  4 
Technic,  general,  3 
Tecto-spinal  tract,  417,  452,  464,  467 
Tectum  mesencephali,  415 
Teeth,  200 

blood-vessels  of,  206 
cementum  of,  200,  204,   212 
circular  dentoid  ligament,  205 
crown  of,  200 
cuticula  dentis,  204 
dental  canals,  201,  21  r 
germ,  206 
groove,  206,  209 
papilla,  206 
periosteum,  205 
ridge,  208 
sac,  208,  211 
dentinal  fibres,  201 

pulp,  201 
dentine  of,  200,  201 
development  of,  206,  212 
common  dental  germ,  206 
cuticular  membrane,  209 
dental  papilla,  206 

ridge,  208 
enamel  organ,  206 
special  dental  germ,  206 
technic  of,  212 
Tomes'  process,  209 
enamel  of,  200,  204,  208 
cells,  2og 
fibres,  204,  205 
organ,  206,  20S 
prisms,  204,  2og 
fang  of,  200 

incremental  lines  of  Schreger,  202 
interglobular  spaces,  203,  2ri 
lines  of  Retzius,  204 
lymphatics  of,  206 
milk,  200 
nerves  of,  206 

Neumann's  dental  sheath,  203 
odontoblasts  of,  201.  206 
peridental  membrane,  205 
]:)ermanent,  20S,  211 
pulp  cavity,  200 


oS4 


INDEX. 


Teeth,  root  of,  200 
canal  of,  200 

special  dental  germs,  206 

technic  of,  212 

Tomes'  granular  layer,  204 
process,  209 

true  molars,  212 
Tegmentum,  374,  427,  431,  447 

brachia  conjunctiva,  465 

central  tegmental  tract,  439,  447, 

454,  464 

development  of,  374 

fillet,  397 

fourth  cranial  nerve,  464,  465 

lateral  lemniscus,  397 

nucleus  ruber,  465 

posterior  longitudinal  fasciculus, 
467 

reticular  formation,  467 

superior  coUiculi,  467 
peduncles,  465 
Telencephalon,  373 
Telophase,  5 1 
Tendon,  structure  of,  78 

sheaths,  184 
Tendon-muscle  junction,  184 

organs  of  Golgi  in,  390 

peripheral-nerve  terminations  in, 
388 
Tenon,  capsule  of,  512 
Tensor  chorioideae,  500 
Terminal  arborizations,  117 

bronchus,  274 

nucleus,  438 
Terminations,  nerve,  385 

annular,  388 

arborescent,  388 

Ruffini's  theory  of,  388 

spiral,  388 
Testis,  303 

blood-vessels  of,  312 

corpus  Highmori,  303 

development  of,  349 

ducts  of,  309 

epididymis  of,  303 

lobules  of,  303 

lymphatics  of,  312 

mediastinum,  303 

nerves,  3  13 

secretion  of,  3  r  3 

semen,  3  13 

seminal  ducts  of,  309; 


Testis,  seminiferous  tubules  of,  304 

spermatozoa,  307,  313 

technic  of,  3  16 

tunica  albuginea  of,  303 
vaginalis,  303 
vasculosa,  303 

vas  deferens,  304 
Thalamencephalon,  468 
Thalamo-cortical  neurones,   414,  469 

470 
Thalamus,  468,  470 

anterior  peduncle  of,  481 

bundle  of  Vicq  d'Azyr,  469 

external  segment  of,  469 

internal  segment  of,  469 

mamillo-thalamic  tract,  469 

nuclei  of,  468,  469 

nucleus  of  Luys,  469 

Sachs,    E.,   concerning  the,   469, 
470 

thalamic    radiations,    469,     470, 
472 
Theca  folliculi,  326 
Thermostat,  1 2 
Thermotaxis,  46 
Thionin,  17 

Thoma,  ampulla  of,  162 
Thomas,  fasciculus  of,  418 
Thoracic  duct,  143 

technic  for,  145 
Three-neurone  afferent  suprasegmen- 
tal  conduction  path,  378 

spinal  reflex  arc,  421,  435,  452 
Thrombocytes,  98 
Thymus,  153 

blood-vessels  of,  155 

developraent  of,  153 

Hassall's  corpuscles,  154 

lymphatics  of,  155 

nerves  of,  155 

technic,  155 
Thyreoid,  280 

absence  of,  282 

blood-vessels  of,  282 

cartilage,  266 

cells  of,  281 

colloid  of,  281 

development  of,  282 

isthmus  of,  281 

lymjjhatics  of,  282 

nerves  of,  282 

technic,  285 


INDEX. 


5S.3 


Tiniofeew,     concerning    nerve     fibres 

in  prostate  gland,  318 
Tissue,  connective,   73;  see  also  Con- 
nective tissue 

elements,  dissociation  of,  4 
Tissues,  59 

adipose,  85 

blood,  95 

bone,  92 

cartilage,  89 

classification  of,  61 

connective,  73 

derivatives  from  ectoderm,  ento- 
derm, mesoderm,  61 

dissociation  of,  4 

elastic,  78 

endothelium,  70 

epithelial,  63 

erectile,  319,  345,  346     • 

examination  of  fresh,  4 

fat,  85 

general     references     for     further 
study  of,  127 

histogenesis  of,  61 

lymphatic,  84 

mesothelium,  70 

rauscle,  10 1 

nerve,  1 1 1 

osteogenetic,  173 

subcutaneous,  352 

subserous,  235 
Toluidin  blue,  17 
Toluol,  as  solvent,  13 
Tomes'  granular  layer,  202 

process,  209 
Tongue,  196 

blood-vessels  of,  199 

circumvallate  papillae,  198 

connective  tissue  of,  197 

Ebner's  glands,  199 

end-bulbs  of  Krause,  200 

fibres  of,  196 

filiform  papillas,  197 

fungiform  papillae,  198 

glands  of,     199 

longitudinal  fibres  of,  197 

lymph  follicles  of,  157,  199 
spaces  of,  199 

muscles  of,  196 

nerves  of,  200 

papillae  of,  197 

septum  linguae,  197 


Tongue,    taste   buds,    199,     200,    3S7, 

technic  of,  200 

transverse  fibres  of,  196 

vertical  fibres  of,  196 
Tonsils,  155 

blood-vessels  of,  158 

crypts  of,  156 

development  of,  157 

lingual;  folliculas  linguales,  157 
foramen  caecum  lingui  of,  157 

lymphatics  of,  158 

l3^mphoid   infiltration   of   epithe- 
lium, 157 

nerves  of,  158 

nodule  of,  156 

germ  centre  of,  156 

palatine  or  true,  155 

pharyngeal,  157 
adenoids  of,  157 

salivary  corpuscles  of,  157 

technic  of,  158 
Trachea,  266 

blood-vessels  of,  2 68 

cartilages  of,  267 

glands  of,  267 

lymphatics  of,  269 

muscle  cells  of,  268 

nerves  of,  269 

technic  of,  269 
Tract,  antero-lateral  ascending — ven- 
tral spino-cerebellar,  415 

anterio-lateral  descending,  41S 

Burdach's,  408,  414 

central  tegmental,  439,  447,  454, 
464 

cochlear,  450,  452 

comma,  of  Schultze,  419 

cortico-spinalis,   416 

crossed  pyramidal,  416 

descending,     from     Deiter's    nu- 
cleus, 418,  435 
from     interstitial     nucleus     of 

Cajal,  417,  433,  435 
from  vestibular  nuclei,  41S 

direct  cerebellar,  415 
pyramidal,  417 

dorsal  spino-cerebellar,  415,  426, 

433.  45°.  452,  454 
dorso-lateral     ascending — dorsal 

spino-cerebellar,  415 
fasciculus  of  Thomas,  418 


586 


INDEX. 


Tract,  fundamental  or  ground  bundles, 

399.  419 

Flechsig's,  415 

Goll's,  408,  414 

Gowers',  416 

Helweg's,  418 

Lissauer's,  397,  403 

long    ascending    arms    of    dorsal 
root  fibres,  413 

raamillo-thalamic,  469 

marginal    bundle    of    Lowenthal, 
418 

oval  bundle  of  Flechsig,  418 

pallio-spinalis,  416 

posterior,  414 
funiculi,  413 

pyramidal,  416 

reticulo-spinalis,  433 

rubro-spinal,  417,  433,  435,  447 

secondary  cochlear,  44 1 
vestibular,  441 

septo-marginal,  418 

short  fibre,  399 

spinalis  trigemini,  433 

spino-cerebellar,      ventral,      415, 
426,  433,  450,  452,  453,  464 

spino-tectal,  415 

spino-thalamic,     414,     431,     45°, 
452,  453.  465.  470 

tecto-spinal,  417 

Turck's,  417 

uncrossed  cerebellar,  415 

Von  Monakow's,  417 
Tractus,  see  Tract 
Transitional  leucocytes,  97 
Transverse  temporal  gyri  of  Heschl, 

485 
Trapezoid  nucleus,  441 
Trapezium,  44  i 

Trigeminus  (V  nerve),  425,  492 
Trigonum,  6r 

olfactorium,  477 
Trochlearis  (IV  nerve),  462,  464,  492 
Trophospongium,  42 
True  corpora  lutea,  330 

tonsils,  155 
Tuberculum  cinereum,  430,  477 

olfactorium,  477 
Tubules,  arched,  29;,  293 

collecting,  29;,  293 

distal,  29  f,  292 

first  or  i^roximal,  290,  292 


Tubules,  intercalated,  243 

salivary,  242 

second  or  distal,   291,   292 

secreting,  242 

seminiferous,  304 

straight,  291,   293,  308 

uriniferous,  288 
Tubulo-alveolar  gland,  248 
Tunica  albuginea,  of  ovary,  324 
of  penis,  319 
of  testis,  303 

dartos,  352 

propria,    of  mucous   membranes, 
191 

vaginalis,  303 

vasculosa,  303 
Two-neurone   spinal   reflex   arc,    420, 

452 
Tympanic  membrane,  519 
Tympanum,  519;  see  also  Ear,  middle 
Tyson,  glands  of,  321 


Ultimate  fibrillae,  103 
Uncinate  fasciculus,  479,  481 
Unipolar  nerve  cells,   112 
Ureter,  297 

blood-vessels  of,  297 

coats  of,  297 

development  of,  346 

glands  of,  297 

lymphatics  of,  297 

nerves  of,  297 

technic  of,  349 
Urethra,  female,  321 

glands  of  Littre  of,  321 

male,  321 

fossa  navicularis,  322 
glands  of  Littre  of,  322 
technic  of,  322 
Urinary  bladder,  298 

blood-vessels  of,  299 

cells  of,  298 

development  of,  346 

c])ithelium  of,  298 

fllirous  layer  of,  299 

lymjjhatics  of,  299 

muscular  layers  f)f,  2(;() 

mucous  membrane  of,  298 

nerves  of,  299 

system,  286 

development  of,  30 j,  346 


IXDEX. 


587 


Urinary  system,  kidney,  286 
pelvis,  297 
suprarenal  gland,  299 
ureter,  297 
urinary  bladder,  298 
technic  of,  302 
Uriniferous  tubule,  288 

arched  tubule  of,  289,  291 
ascending   arm   of   Henle's   looj), 

288,  291 
blood-vessels  of,  293 
Bowman's  capsule,  290 
descending  arm  of  Henle's  loop, 

288,  290 
development  of,  288 
duct  of  Bellini,  289 
epithelium  of,  292,  293 

first     or     proximal     convoluted, 

289,  290 
foramina  papillaria,  289 
glomerulus,  288,  289 
Henle's  loop,  263,  288 
location  in  kidney  of,  292 
Malpighian  body,  288,  289 
meinbrana  propria  of,  289 
neck  of,  290 

renal  corpuscle,   288 

Rlihle,  concerning,  293 

second  or  distal  convoluted,  289, 

291 
straight  or  collecting,  289,  291 
Uterus,  336 

blood-vessels  of,  344 
cervix,  337 
coats  of,  336 
decidua  basalis,  340 

capsularis,  340 

graviditatus,  340 

menstrualis,  339 

reflexa,  340 

serotina,  340 

subchorionic  placental,  344 

vera,  340 
decidual  cells  of,  340 
development    of,    346;    see    also 
Reproductive  system,  develop- 
ment of 
lymphatics  of,  345 
masculinus,  3  1  8 
mucosa  of  menstruating,  338 

of  pregnant,  340 

of  resting,  337 


Uterus,  muscle  cells  of,  337 

stratum  submucosum,  336 
supravasculare,  336 
vasculare,  336 
nerves  of,  345 
placenta,  341 
pregnant,  340 

theories  concerning,  340 
stage    of     menstruation     jjroper, 

339 

of  preparation,  338 

of  reparation,  339 
techriic  of,  349 
with  placenta  in  situ,  technic  of. 

Utricle,  521;     see    also    Saccule    and 

utricle 
Utriculo-saccular  duct,  521 
Utriculus  prostaticus,  317,  318 
Uvula,  mucous  membrane  of,  193 


Vagina,  345 

blood-vessels  of,  345 

coats  of,  345 

lymphatics  of,  346 

nerves  of,  346 

rugag  of,  345 

technic  of,  350 
Vagus  nerve,  425,  437,  492 
Valve,  Heisterian,  260 
Valves  of  heart,  141 

of  veins,  138 
Valvulae  conniventes,  216 
Vas  deferens,  309,  310 
technic  of,  317 

epididymis,  309 
Vasa  efferentia,  309,  347 

vasorum,  139 
Vascular  papillae,  352 

system,  131;  see  also  Circulatory 
system 
Vater-Pacinian  cor]Hiscles,  365 
Veins,  137 

adventitia  of,  138 

arcuate,  296 

central,  255 

coats  of,  137 

development  of,  142 

intima  of,  138 

lymph  channels  of,  139 

media  of,  138 


588 


INDEX. 


Veins,  musculature  of,  138 
nerves  of,  139 
perivascular    lymph     spaces    of, 

139 

portal,  254 

renal,  286 

splenic,  160 

stellate,  of  Verheyn,  296 

sublobular,  255 

technic  of,  139 

valves  of,  138 

vasa  vasorum,  139 

venae  vorticosae,  497 
Venas  vorticosse,  497 
Ventral  spino-cerebellar  tract,  414 
Ventricle,  fourth,  374,  430,  437,  447 

chorioid  plexuses  of,  374 

muscle  of,  140 
Verheyn,  stellate  veins  of,  296 
Vermiform  appendix,  232 
coats  of,  232 
lymph  nodules  of,  234 
mesoappendix,  233 
technic  of,  241 
Vermis  of  cerebellum,  415,  449,  455 
Vesicle,  air,  274 

brain,  373 

germinal,  53 

optic,  515 

otic,  529 

seminal,  311 
Vesicula  prostatica,  317 
Vestibular  ganglion,  425 

nerve,  425,  441 

nuclei,  441 

descending  tract  from,  441 
Vestibule,  520 

ductus  reuniens  of,  521 

endolymphatic  duct,  521 

saccule  of,  521 

utricle  of,  521 

utriculo-saccular  duct  of,    521 
Vicq  d'Azyr,  bundle  of,  469 
Villi,  224,  237,  341 

development  of,  262 

lacteals  of,  240 

synovial,  18  r 
Visceral  neurones,  376,  425 

peritoneum,  192 
Visual  area,  488 

path,  425,  470,  472,  474,  475,  485, 
488 


Visual  purple,  503 
Vital  properties  of  cells,  45 
function,  46 
irritability,  46 
metabolism,  45 
motion,  46 
reproduction,  47 
Vitreous  body  of  the  eye,  511 
Cloquet's  canal,  511 
hyaloid  canal  of,  511 
membrane  of  chorioid,  498 
of  iris,  501 
Vocal  cords,  266 
Volkmann's  canal,  167,  171 
Voluntary  striated  muscle,     102;    see 

Muscle,  striated,  voluntary 
Von  Bechterew's  nucleus,  448,  453 
Von  Bibra,  concerning  chemical  com- 
position of  dentine,  201 
Von   Gudden,   concerning  method  of 
determining   fibre   tracts   of 
cord,  413 
Von  Monakow's  bundle,  417 


Wagner,  corpuscles  of,  365 
Walker,  coccygeal  gland,  145 
Wallerian  degeneration,  law  of,    112 
Wandering  cells,  75 
Warthin,  showing  haemolymph  node, 

151,  152 
Washing  after  fixation,  8 
Weigert's  elastic-tissue  stain,  26 
haematoxylin,  17 
method    of    staining    medullated 
nerve  fibres,  29 
Weigert-Pal  method,  30 
Wernicke,  perpendicular  fasciculus  of, 

479 
Wharton's  duct,  244 
Wheeler,  showing  amitosis,  47 
White  blood  cells  (leucocytes),  96 
White  matter,  377,  403 

rami    communicantes,    381,    390, 
301,  395 
Wilson,  E.  B.,  diagrams  showing  mi- 
tosis, 48,  49 
Wirsung,  duct  of,  247 
Wolffian  body,  308,  347 
bodies,  347 
ridges,  346 
Wrisburg,  cartilage  of,  266 


INDEX. 


589 


Xylol  and  cajeput  oil  for  clearing, 

-balsam,  21 

damar,  28 
Xylol-paraffin  for  embedding,    13 


Yolk  granules,  328,  330 


Zenker's  fluid  for  decalcifying,  9 

for  fixation,  8 
Zinn,  Zonule  of,  510 


Zona  incerta,  472 
pectinata,  525 
pellucida,  55,  327 
spongiosa,  402,  403 
tecta,  525 
Zone  of  Lissauer,  397,  40J 
of  oval  nuclei,  265 
of  round  nuclei,  265 
Zonula  ciliaris,  510 
Zonule  of  Zinn,  510 
Zymogen  granules,  24S 
technic  of,  252 


Y^^o^ 


^Msi^Wtf^^^v 


